Gaussian Measures and Representations of the Holonomy-Flux Algebra - Nekovar, Stefan; Sahlmann, Hanno (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2014)
Gaussian path integrals play an important role for free quantum field theories, and for the perturbative treatment of interacting quantum field theories. These path integrals are defined via measures on linear spaces. For loop quantum gravity, a framework for path integrals over spaces of connections was developed. Some examples of what one could call Gaussian measures are known. They are interesting, among other things, because they give the connections finite quantum mechanical fluctuations. In the present thesis, we give a general definition of a Gaussian measure over (Abelian) connections, and study their properties. In particular, we define the holonomy-flux Weyl algebra for U(1). Then we investigate the absolute continuity of Gaussian measures with respect to representations of the Weyl algebra and the unitary implementation of gauge transformations. This shows that for a large subclass, the lengthlike Gaussian measures, there are no representations in which the exponentiated fluxes are implemented unitarily. We also determine some structural properties of Gaussian measures which are invariant under Euclidean transformations of the base manifold. As a side result, we discuss how new methods from analysis can be employed to show, how results obtained with well known algebraic techniques can be reproduced and strengthened using recent results on the convergence of Fourier series.

GENERALIZED BOUNDARY-CONDITIONS FOR GENERAL-RELATIVITY FOR THE ASYMPTOTICALLY FIAT CASE IN TERMS OF ASHTEKARS VARIABLES - Thiemann, Thomas (Classical and Quantum Gravity, 1995)
There is a gap that has not been filled since the formulation of general relativity in terms of Ashtekar's new variables, namely the treatment of asymptotically flat field configurations that are general enough to be able to define the generators of the Lorentz subgroup of the asymptotic Poincare group. While such a formulation already exists for the old geometrodynamical variables, up to now only the generators of the translation subgroup have been able to be defined, because the function spaces of the fields considered earlier are taken in too special a form. The transcription of the framework from the ADM variables to Ashtekar's variables turns out not to be straightforward, due to the a priori freedom to choose the internal SO(3) frame at spatial infinity, and due to the fact that the non-trivial reality conditions of the Ashtekar framework re-enter the stage when imposing suitable boundary conditions on the fields and the Lagrange multipliers.

General relation between stacking order and Chern index: A topological map of minimally twisted bilayer graphene - Theil, Simon; Fleischmann, Maximilian; Gupta, R.; Rost, Fabian; Wullschläger, Florian; Sharma, S.; Meyer, Bernd; Shallcross, S. (Physical Review B, 2021)
We derive a general relation between the stacking vector u describing the relative shift of two layers of bilayer graphene and the Chern index. We find C = nu(1 - sign(vertical bar V-AB vertical bar - vertical bar V-BA vertical bar)), where nu is a valley index and vertical bar V-alpha beta vertical bar the absolute value of the u dependent stacking potentials that uniquely determine the interlayer interaction; AA stacking plays no role in the topological character. With this expression we show that while ideal and relaxed minimally twisted bilayer graphene appear so distinct as to be almost different materials, their Chern index maps are, remarkably, identical. The topological physics of this material is thus strongly robust to lattice relaxations.
CRIS-Team WoS Importer:2021-09-17

Genus dependence of the number of (non-)orientable surface triangulations - Krüger, Benedikt; Mecke, Klaus (Physical Review D, 2016)
which might guide a mathematician's proof for the exact asymptotics.

Geometrical Clocks in Cosmological Perturbation Theory - Herzog, Adrian; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2017)

Geometric effects in random assemblies of ellipses - Lovrić, Jakov; Kaliman, Sara; Barfuß, Wolfram; Schröder-Turk, Gerd E.; Smith, Ana-Suncana (Soft Matter, 2019)
Assemblies of anisotropic particles commonly appear in studies of active many-body systems. However, in two dimensions, the geometric ramifications of the finite density of such objects are not entirely understood. To fully characterize these effects, we perform an in-depth study of random assemblies generated by a slow compression of frictionless elliptical particles. The obtained configurations are then analysed using the Set Voronoi tessellation, which takes the particle shape into account. Not only do we analyse most scalar and vectorial morphological measures, which are commonly discussed in the literature or which have recently been addressed in experiments, but we also systematically explore the correlations between them. While in a limited range of parameters similarities with findings in 3D assemblies could be identified, important differences are found when a broad range of aspect ratios and packing fractions are considered. The data discussed in this study should thus provide a unique reference set such that geometric effects and differences from random assemblies could be clearly identified in more complex systems, including ones with soft and active particles that are typically found in biological systems.
CRIS-Team Scopus Importer:2019-11-12

Geometric meaning of the Penrose metric - Sahlmann, Hanno; Wolz, Florian (2014)

Geometric properties of the Livine-Speziale coherent intertwiner - Sahlmann, Hanno; Seeger, Robert; Seeger, Robert (2015)

Geometrische Eigenschaften der Verschränkungsentropie in der Loop-Quantengravitation - Stritzelberger, Nadine; Sahlmann, Hanno (2014)

Geometry and entanglement entropy of surfaces in loop quantum gravity - Sahlmann, Hanno; Grüber, David; Zilker, Thomas (Physical Review D, 2018)

Geometry of four-valent spin networks with spin 1/2 - Stumpf, Henning; Sahlmann, Hanno (2013)

Geometry: The leading parameter for the Poisson's ratio of bending-dominated cellular solids - Mitschke, Holger; Schury, Fabian; Mecke, Klaus; Wein, Fabian; Stingl, Michael; Schroder-Turk, Gerd E. (International Journal of Solids and Structures, 2016)
Control over the deformation behaviour that a cellular structure shows in response to imposed external forces is a requirement for the effective design of mechanical metamaterials, in particular those with negative Poisson's ratio. This article sheds light on the old question of the relationship between geometric microstructure and mechanical response, by comparison of the deformation properties of bar-and-joint frameworks with those of their realisation as a cellular solid made from linear-elastic material. For ordered planar tessellation models, we find a classification in terms of the number of degrees of freedom of the framework model: first, in cases where the geometry uniquely prescribes a single deformation mode of the framework model, the mechanical deformation and Poisson's ratio of the linearly-elastic cellular solid closely follow those of the unique deformation mode; the result is a bending-dominated deformation with negligible dependence of the effective Poisson's ratio on the underlying material's Poisson's ratio and small values of the effective Young's modulus. Second, in the case of rigid structures or when geometric degeneracy prevents the bending-dominated deformation mode, the effective Poisson's ratio is material-dependent and the Young's modulus (E) over tilde (cs) large. All analysed structures of this type have positive values of the Poisson's ratio and large values of (E) over tilde (cs). Third, in the case, where the framework has multiple deformation modes, geometry alone does not suffice to determine the mechanical deformation. These results clarify the relationship between mechanical properties of a linear-elastic cellular solid and its corresponding bar-and-joint framework abstraction. They also raise the question if, in essence, auxetic behaviour is restricted to the geometry-guided class of bending-dominated structures corresponding to unique mechanisms, with inherently low values of the Young's modulus. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Cellular structures; Homogenisation; Floppy frameworks; Auxeticity; Mechanical metamaterial

Glycerol as a Substrate and Inactivator of Coenzyme B-12-Dependent Diol Dehydratase - Bilic, Luka; Baric, Danijela; Sandala, Gregory M.; Smith, David Mathew; Kovacevic, Borislav (Chemistry - A European Journal, 2021)
Diol dehydratase, dependent on coenzyme B-12 (B-12-dDDH), displays a peculiar feature of being inactivated by its native substrate glycerol (GOL). Surprisingly, the isofunctional enzyme, B-12-independent glycerol dehydratase (B-12-iGDH), does not undergo suicide inactivation by GOL. Herein we present a series of QM/MM and MD calculations aimed at understanding the mechanisms of substrate-induced suicide inactivation in B-12-dDDH and that of resistance of B-12-iGDH to inactivation. We show that the first step in the enzymatic transformation of GOL, hydrogen abstraction, can occur from both ends of the substrate (either C1 or C3 of GOL). Whereas C1 abstraction in both enzymes leads to product formation, C3 abstraction in B-12-dDDH results in the formation of a low energy radical intermediate, which is effectively trapped within a deep well on the potential energy surface. The long lifetime of this radical intermediate likely enables its side reactions, leading to inactivation. In B-12-iGDH, by comparison, C3 abstraction is an endothermic step; consequently, the resultant radical intermediate is not of low energy, and the reverse process of reforming the reactant is possible.
CRIS-Team WoS Importer:2021-05-14

Goodness-of-fit tests for complete spatial randomness based on Minkowski functionals of binary images - Ebner, Bruno; Henze, Norbert; Klatt, Michael A.; Mecke, Klaus (Electronic Journal of Statistics, 2018)
We propose a class of goodness-of-fit tests for complete spatial randomness (CSR). In contrast to standard tests, our procedure utilizes a transformation of the data to a binary image, which is then characterized by geometric functionals. Under a suitable limiting regime, we derive the asymptotic distribution of the test statistics under the null hypothesis and almost sure limits under certain alternatives. The new tests are computationally efficient, and simulations show that they are strong competitors to other tests of CSR. The tests are applied to a real data set in gamma-ray astronomy, and immediate extensions are presented to encourage further work.
CRIS-Team WoS Importer:2019-03-22

Grand canonical simulations of hard-disk systems by simulated tempering - Mecke, Klaus; et al. (International Journal of Modern Physics C, 2004)
The melting transition of hard disks in two dimensions is still an unsolved problem and improved simulation algorithms may be helpful for its investigation. We suggest the application of simulating tempering for grand canonical hard-disk systems as an efficient alternative to the commonly-used Monte Carlo algorithms for canonical systems. This approach allows the direct study of the packing fraction as a function of the chemical potential even in the vicinity of the melting transition. Furthermore, estimates of several spatial characteristics including pair correlation function are studied in order to test the accuracy of the method and to analyze the melting transition in hard-disk systems. Our results seem to show that there is a weak first-order phase transition.
Keywords: hard-disk model; phase transition; metropolis hastings; simulated tempering

Gravitational dynamics for all tensorial spacetimes carrying predictive, interpretable, and quantizable matter - Giesel, Kristina; Schuller, Frederic; Witte, Christof; Wolfarth, Matthias (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012)
Only a severely restricted class of tensor fields can provide classical spacetime geometries, namely those that can carry matter field equations which are predictive, interpretable, and quantizable. These three conditions on matter translate into three corresponding algebraic conditions on the underlying tensorial geometry: the latter must be hyperbolic, time-orientable, and energy-distinguishing. Lorentzian metrics, on which general relativity and the standard model of particle physics are built, present just the simplest tensorial spacetime geometry satisfying these conditions. The problem of finding gravitational dynamics-for the general tensorial spacetime geometries satisfying the above minimum requirements-is reformulated in this paper as a system of linear partial differential equations, in the sense that their solutions yield the actions governing the corresponding spacetime geometry. Thus, the search for modified gravitational dynamics is reduced to a clear mathematical task.

Gravitationally induced decoherence in open quantum systems using linearised gravity formulated in Ashtekar variables. - Fahn, Max Joseph (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2020)

gravitationally induced decoherence on quantum vector fields - Kemper, Roman; Giesel, Kristina; Fahn, Max Joseph (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2023)
In this thesis we consider the coupling of Maxwell theory to linearised gravity and derive a master equation which suggests gravitationally induced decoherence on vector fields. The model is based on the linear Hamiltonian formulation of general relativity with the use of Ashtekar variables. The matter is coupled to linearised gravity, consistently using the framework of post-Minkowski formalism. In order to formulate the model at the gauge invariant level, the relational formalism is used. Therefore, we will consistently connect linearised gravity to the constrained system of Maxwell’s theory by constructing suitable geometrical and electromagnetic reference fields. This will be used to construct Dirac observables for the coupled system. Then we will use a reduced phase space quantisation on the Fock space. To construct a TCL master equation we apply the projecting operator technique with the time-convolutionless approach to the model, using a Gibbs state as the initial state for linearised gravity. All assumptions and approximations in the intermediate steps will be carefully analysed. In addition, the final TCL master equation is formulated in terms of thermal Wightmann functions and is not automatically of the Lindblad type, which is often the starting point for phenomenological models, and in contrast to the existing literature. For the derived master equation, we will also discuss why the Markov approximation is not easily applicable. Furthermore, we will motivate that the formalism used in this thesis to couple a constrained system to linearised gravity could be generalised to all Yang-Mills theories.<br
Keywords: Open quantum systems; quantum gravity; relational formalism

Gravity, geometry, and the quantum - Sahlmann, Hanno (Springer Handbook of Spacetime, 2014)

Gravity quantized: Loop quantum gravity with a scalar field - Giesel, Kristina; Domagala, Marcin; Kaminski, Wojciech; Lewandowski, Jerzy (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2010)
..."but we do not have quantum gravity." This phrase is often used when analysis of a physical problem enters the regime in which quantum gravity effects should be taken into account. In fact, there are several models of the gravitational field coupled to (scalar) fields for which the quantization procedure can be completed using loop quantum gravity techniques. The model we present in this paper consists of the gravitational field coupled to a scalar field. The result has similar structure to the loop quantum cosmology models, except that it involves all the local degrees of freedom of the gravitational field because no symmetry reduction has been performed at the classical level.

Group theory of circular-polarization effects in chiral photonic crystals with four-fold rotation axes applied to the eight-fold intergrowth of gyroid nets - Saba, Matthias; Turner, Mark D.; Mecke, Klaus; Gu, Min; Schröder-Turk, Gerd (Physical Review B, 2013)
We use group or representation theory and scattering matrix calculations to derive analytical results for the band structure topology and the scattering parameters, applicable to any chiral photonic crystal with body-centered-cubic symmetry I432 for circularly polarized incident light. We demonstrate in particular that all bands along the cubic [100] direction can be identified with the irreducible representations E-+/-, A, and B of the C-4 point group. E+ and E- modes represent the only transmission channels for plane waves with wave vector along the Delta line, and E- and E+ are identified as noninteracting transmission channels for right-and left-circularly polarized light, respectively. Scattering matrix calculations provide explicit relationships for the transmission and reflectance amplitudes through a finite slab which guarantee equal transmission rates for both polarizations and vanishing ellipticity below a critical frequency, yet allowing for finite rotation of the polarization plane. All results are verified numerically for the so-called 8-srs geometry, consisting of eight interwoven equal-handed dielectric gyroid networks embedded in air. The combination of vanishing losses, vanishing ellipticity, near-perfect transmission, and optical activity comparable to that of metallic metamaterials makes this geometry an attractive design for nanofabricated photonic materials.

Growth Modes of Quasicrystals - Achim, Cristian; Schmiedeberg, Michael; Löwen, Hartmut (Physical Review Letters, 2014)
The growth of quasicrystals, i.e., aperiodic structures with long-range order, seeded from the melt is investigated using a dynamical phase field crystal model. Depending on the thermodynamic conditions, two different growth modes are detected, namely defect-free growth of the stable quasicrystal and a mode dominated by phasonic flips which are incorporated as local defects into the grown structure such that random tilinglike ordering emerges. The latter growth mode is unique to quasicrystals and can be verified in experiments on one-component mesoscopic systems.

Growth of high-quality homoepitaxial diamond films by HF-CVD - Stammler, Markus; Eisenbeiß, Henrick; Ristein, Jürgen; Neubauer, Jürgen; Göbbels, Matthias; Ley, Lothar; Ristein, Jürgen; Ley, Lothar (Diamond and Related Materials, 2002)
Defined growth of high-quality crystalline diamond films is necessary for manufacturing of electronic devices. Several groups have already worked on this topic and the main challenges remaining are the suppression of crystalline defects, the reduction of impurities and higher growth rates. High-quality homoepitaxial diamond films were produced in a hot filament chemical vapor deposition (HF-CVD) system with and without addition of nitrogen to the gas phase. Substrates were (100)-oriented synthetic Ib diamonds (Sumitomo) with a maximum misorientation angle of 0.3° as determined by X-ray diffraction. By adjusting the α parameter independently to a value close to two using polycrystalline diamond films on silicon growth rates of up to 500 nm/h could be achieved while simultaneously keeping the density of unepitaxial crystallites below 10 cm-2. The surface roughness (RMS) was below 1 nm in a 1 × 1-μm2 area. Impurities were studied by photoluminescence and cathodoluminescence spectroscopy. For the films deposited without intentional nitrogen addition, nitrogen-related impurities could only be detected by low temperature photoluminescence indicating a very low concentration. At 1.68 eV we observed the signature of the Si-vacancy complex probably caused by evaporation of Si from the tungsten filament. © 2002 Elsevier Science B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2002.nat.dgeo.IGM.LM.growth
Keywords: Diamond growth and characterization; HF-CVD; Homoepitaxy; Luminescene

Growth of two-dimensional decagonal colloidal quasicrystals - Martinsons, Miriam; Schmiedeberg, Michael (Journal of Physics: Condensed Matter, 2018)

Growth of two-dimensional dodecagonal colloidal quasicrystals: Particles with isotropic pair interactions with two length scales vs. patchy colloids with preferred binding angles - Gemeinhardt, Anja; Martinsons, Miriam; Schmiedeberg, Michael (European Physical Journal E, 2018)

Hamiltonian Constraint in Loop Quantum Gravity - Liegener, Klaus; Thiemann, Thomas (2012)

Hamiltonian diagonalization in hybrid quantum cosmology - Navascues, Beatriz Elizaga; Mena Marugan, Guillermo A.; Thiemann, Thomas (Classical and Quantum Gravity, 2019)
We explore the possibility of selecting a natural vacuum state for scalar and tensor gauge-invariant cosmological perturbations in the context of hybrid quantum cosmology, by identifying those variables for the description of the perturbations that display a dynamical behavior adapted in a specific way to the evolution of the entire cosmology. We make use of a canonical formulation of the whole of the cosmological system (background geometry and perturbations) in which the perturbative gauge-invariant degrees of freedom are identified as canonical variables. Introducing background-dependent linear canonical transformations that respect the spatial symmetries of the background on these perturbations and completing those canonical transformations for the entire system, we are able to characterize a generic collection of annihilation and creation like variables that obey the dynamics dictated by a respective collection of Hamiltonians. We then impose that such Hamiltonians possess no self-interaction terms so that, in a Fock representation with normal ordering, they act diagonally on the basis of n-particle states. This leads to a semilinear first-order partial differential equation with respect to the background for the coefficients that define the annihilation and creationlike variables for all Fourier modes, as well as to a very precise ultraviolet characterization of them. Such first-order equation contains, in the imaginary part of its complex solutions, the complicated second-order field equation that typically arises for the time-dependent frequency of the perturbations in the context of quantum field theory in curved spacetimes. We check that the asymptotic knowledge acquired allows one to select the standard vacua in Minkowski and de Sitter spacetimes. Finally, we discuss the relation of our vacuum and the standard adiabatic vacua, and check that our asymptotic characterization of variables with a diagonal Hamiltonian displays the properties that would be desirable for an adiabatic state of infinite order.
CRIS-Team WoS Importer:2019-09-13

Hamiltonian Renormalization V: Free Vector Bosons - Liegener, Klaus; Thiemann, Thomas (Frontiers in Astronomy and Space Sciences, 2021)
In a recent proposal we applied methods from constructive QFT to derive a Hamiltonian Renormalization Group in order to employ it ultimately for canonical quantum gravity. The proposal was successfully tested for free scalar fields and thus a natural next step is to test it for free gauge theories. This can be done in the framework of reduced phase space quantization which allows using techniques developed earlier for scalar field theories. In addition, in canonical quantum gravity one works in representations that support holonomy operators which are ill defined in the Fock representation of say Maxwell or Proca theory. Thus, we consider toy models that have both features, i.e. which employ Fock representations in which holonomy operators are well-defined. We adapt the coarse graining maps considered for scalar fields to those theories for free vector bosons. It turns out that the corresponding fixed pointed theories can be found analytically.
CRIS-Team WoS Importer:2021-03-05

Hard and bright gamma-ray emission at the base of the Fermi bubbles - Herold, Laura; Malyshev, Dmitry (Astronomy & Astrophysics, 2019)
Context. The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to 55◦ in latitude above and below the Galactic center (GC). Although the FBs were discovered eight years ago, their origin and the nature of the gamma-ray emission are still unresolved. Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin. Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC. Aims. We analyze nine years of Fermi Large Area Telescope data in order to study in more detail than the previous analyses the gamma-ray emission at the base of the FBs, especially at energies above 10 GeV. Methods. We used a template analysis method to model the observed gamma-ray data and calculate the residual emission after subtraction of the expected foreground and background emission components. Since there are large uncertainties in the determination of the Galactic gamma-ray emission toward the GC, we used several methods to derive Galactic gamma-ray diffuse emission and the contribution from point sources to estimate the uncertainties in the emission at the base of the FBs. Results. We confirm that the gamma-ray emission at the base of the FBs is well described by a simple power law up to 1 TeV energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV. It has larger intensity than the FBs emission at high latitudes and is shifted to the west (negative longitudes) from the GC. If the emission at the base of the FBs is indeed connected to the high-latitude FBs, then the shift of the emission to negative longitudes disfavors models in which the FBs are created by the supermassive black hole at the GC. We find that the gamma-ray spectrum can be explained either by gamma rays produced in hadronic interactions or by leptonic inverse Compton scattering. In the hadronic scenario, the emission at the base of the FBs can be explained either by several hundred supernova remnants (SNRs) near the GC or by about ten SNRs at a distance of ∼1 kpc. In the leptonic scenario, the necessary number of SNRs that can produce the required density of CR electrons is a factor of a few larger than in the hadronic scenario.
CRIS-Team Scopus Importer:2021-04-20
Keywords: Astroparticle physics; Galaxy: bulge; Galaxy: center; Gamma rays: diffuse background; ISM: bubbles; ISM: jets and outflows

Hard-core magnons in the S=1/2 Heisenberg model on the square lattice - Schmidt, Kai Phillip; et al. (Physical Review B, 2006)
We propose a versatile approach to treat commonly arising constraints. It is illustrated for interacting magnons of the Heisenberg antiferromagnet on a square lattice. For systems of LxL sites a nonperturbative continuous unitary transformation (CUT) is used to derive an effective Hamiltonian conserving the number of magnons. They are bosonic particles with a hard-core constraint which is captured by a local, repulsive interaction U. The limits U ->infinity and L ->infinity are achieved by extrapolation. The residual spin gap Delta(1) is smaller than 0.01J reflecting the gapless nature of the magnons. The one-magnon dispersion displays all known characteristics.

Hard-sphere fluids in contact with curved substrates - Mecke, Klaus; et al. (Physical Review E, 2003)
The properties of a hard-sphere fluid in contact with hard-spherical and cylindrical walls are studied. Rosenfeld's density functional theory (DFT) is applied to determine the density profile and surface tension gamma for wide ranges of radii of the curved walls and densities of the hard-sphere fluid. Particular attention is paid to investigate the curvature dependence and the possible existence of a contribution to gamma which is proportional to the logarithm of the radius of curvature. Moreover, by treating the curved wall as a second component at infinite dilution, we provide an analytical expression for the surface tension of a hard-sphere fluid close to arbitrary hard convex walls. The agreement between the analytical expression and DFT is good. Our results show no signs for the existence of a logarithmic term in the curvature dependence of gamma.

Harmonic distortions enhance circular dichroism of dielectric single gyroids - Hielscher, Johannes; Pouya, Caroline; Vukusic, Peter; Schroeder-Turk, Gerd E. (Optics Express, 2017)
The departure from strict periodic order in two-phase dielectric materials can offer properties that are otherwise inaccessible to perfectly ordered photonic crystals. Herewith, we investigate the circular dichroism of the single gyroid photonic crystal in the presence of spatial distortions. FDTD simulations and microwave transmission measurements on 3D-printed replicas show that certain harmonic long-wavelength spatial distortions (chirp) nearly doubles the imbalance of the circular polarisation reflectances, as well as significantly strengthens polarisation-incoherent reflectance. The observed changes are partially rationalised by comparison with simpler distortion models (linear chirp and tetragonal deformation) of the Gyroid.
EAM Import::2019-03-13

Hawking Radiation - Lang, Thorsten; et al. (2011)

Heat and Work Along Individual Trajectories of a Quantum Bit - Naghiloo, M.; Tan, D.; Harrington, P. M.; Alonso Castaneda, Jose Joaquin; Lutz, E.; Romito, A.; Murch, K. W. (Physical Review Letters, 2020)
We use a near quantum limited detector to experimentally track individual quantum state trajectories of a driven qubit formed by the hybridization of a waveguide cavity and a transmon circuit. For each measured quantum coherent trajectory, we separately identify energy changes of the qubit as heat and work, and verify the first law of thermodynamics for an open quantum system. We further establish the consistency of these results by comparison with the master equation approach and the two-projective-measurement scheme, both for open and closed dynamics, with the help of a quantum feedback loop that compensates for the exchanged heat and effectively isolates the qubit.
CRIS-Team WoS Importer:2020-04-07

Herstellung und Charakterisierung stickstoffreicher, qualitativ hochwertiger homo-epitaktischer Diamantfilme mittels Heißdraht-CVD - Eisenbeiß, Henrick; Stammler, Markus; Ristein, Jürgen; Ley, Lothar; Göbbels, Matthias; Neubauer, Jürgen (European Journal of Mineralogy, 2001)
UnivIS-Import:2015-03-09:Pub.2001.nat.dgeo.IGM.LM.herste

Hierarchical quantum master equation approach to charge transport in molecular junctions with time-dependent molecule-lead coupling strengths - Erpenbeck, André; Götzendörfer, Lukas; Schinabeck, Christian; Thoss, Michael (European Physical Journal - Special Topics, 2019)
Time-dependent currents in molecular junctions can be caused by structural fluctuations or interaction with external fields. In this paper, we demonstrate how the hierarchical quantum master equation approach can be used to study time-dependent transport in a molecular junction. This reduced density matrix methodology provides a numerically exact solution to the transport problem including time-dependent energy levels, molecule-lead coupling strengths and transitions between electronic states of the molecular bridge. Based on a representative model, the influence of a time-dependent molecule-lead coupling on the electronic current is analyzed in some detail.
CRIS-Team WoS Importer:2019-04-12

Hierarchical quantum master equation approach to current fluctuations in nonequilibrium charge transport through nanosystems - Schinabeck, Christian; Thoss, M. (Physical Review B, 2020)
We present a hierarchical quantum master equation (HQME) approach, which allows the numerically exact evaluation of higher-order current cumulants in the framework of full counting statistics for nonequilibrium charge transport in nanosystems. The novel methodology is exemplarily applied to a model of vibrationally coupled electron transport in a molecular nanojunction. We investigate the influence of cotunneling on avalanchelike transport, in particular in the nonresonant transport regime, where we find that inelastic cotunneling acts as a trigger process for resonant avalanches, which manifests itself as finite temperature oscillations in the current fluctuations. We also demonstrate that the correction to the elastic noise upon opening of the inelastic transport channel is nonuniversal and strongly affected by the nonequilibrium excitation of the vibration.
CRIS-Team Scopus Importer:2020-03-06

Hierarchical quantum master equation approach to electronic-vibrational coupling in nonequilibrium transport through nanosystems - Schinabeck, Christian; Erpenbeck, André; Haertle, R.; Thoss, Michael (Physical Review B, 2016)
Within the hierarchical quantum master equation (HQME) framework, an approach is presented, which allows a numerically exact description of nonequilibrium charge transport in nanosystems with strong electronic-vibrational coupling. The method is applied to a generic model of vibrationally coupled transport considering a broad spectrum of parameters ranging from the nonadiabatic to the adiabatic regime and including both resonant and off-resonant transport. We show that nonequilibrium effects are important in all these regimes. In particular, in the off-resonant transport regime, the inelastic cotunneling signal is analyzed for a vibrational mode in full nonequilibrium, revealing a complex interplay of different transport processes and deviations from the commonly used G0/2 rule of thumb. In addition, the HQME approach is used to benchmark approximate master equation and nonequilibrium Green's function methods.
EAM Import::2019-03-13

Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point - Hong, Tao; Matsumoto, Masashige; Qiu, Yiming; Chen, Wangchun; Gentile, Thomas R.; Watson, Shannon; Awwadi, Firas F.; Turnbull, Mark M.; Dissanayake, Sachith E.; Agrawal, Harish; Toft-Petersen, Rasmus; Klemke, Bastian; et al. (Nature, 2017)
Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed-matter physics(1-3). The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu-Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics(4,5), is prone to decay into a pair of low-energy Nambu-Goldstone modes in low dimensions(2,6,7). Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using inelastic neutron scattering and applying the bondoperator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S = 1/2 quantum antiferromagnet C9H18N2CuBr4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.

Higgs Mode of Planar Coupled Spin Ladders and its Observation in C9 H18 N2CuBr4 - Ying, T.; Schmidt, Kai Phillip; Wessel, S. (Physical Review Letters, 2019)
Polarized inelastic neutron scattering experiments recently identified the amplitude (Higgs) mode in C9H18N2CuBr4, a two-dimensional near-quantum-critical spin-1/2 two-leg ladder compound, which exhibits a weak easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin structure factor of such planar coupled spin-ladder systems using large-scale quantum Monte Carlo simulations. This allows us to provide a quantitative account of the experimental neutron scattering data within a consistent quantum spin model. Moreover, we trace the details of the continuous evolution of the amplitude mode from a two-particle bound state of coupled ladders in the classical Ising limit all the way to the quantum spin-1/2 Heisenberg limit with fully restored SU(2) symmetry, where it gets overdamped by the two-magnon continuum in neutron scattering.
CRIS-Team Scopus Importer:2019-05-02

Higgs Mode of Planar Coupled Spin Ladders and its Observation in C9H18N2CuBr4 - Ying, T.; Schmidt, Kai Phillip; Wessel, S. (Physical Review Letters, 2019)
Polarized inelastic neutron scattering experiments recently identified the amplitude (Higgs) mode in C9H18N2CuBr4, a two-dimensional near-quantum-critical spin-1/2 two-leg ladder compound, which exhibits a weak easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin structure factor of such planar coupled spin-ladder systems using large-scale quantum Monte Carlo simulations. This allows us to provide a quantitative account of the experimental neutron scattering data within a consistent quantum spin model. Moreover, we trace the details of the continuous evolution of the amplitude mode from a two-particle bound state of coupled ladders in the classical Ising limit all the way to the quantum spin-1/2 Heisenberg limit with fully restored SU(2) symmetry, where it gets overdamped by the two-magnon continuum in neutron scattering.
CRIS-Team WoS Importer:2019-04-12

Higher Dimensional and Supersymmetric Extensions of Loop Quantum Gravity - Thurn, Andreas; Thiemann, Thomas (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2013)

High order perturbation theory for spectral densities of multi-particle excitations: S=1/2 two-leg Heisenberg ladder - Schmidt, Kai Phillip; et al. (European Physical Journal B, 2003)
We present a high order perturbation approach to quantitatively calculate spectral densities in three distinct steps starting from the model Hamiltonian and the observables of interest. The approach is based on the perturbative continuous unitary transformation introduced previously. It is conceived to work particularly well in models allowing a clear identification of the elementary excitations above the ground state. These are then viewed as quasi-particles above the vacuum. The article focuses on the technical aspects and includes a discussion of series extrapolation schemes. The strength of the method is demonstrated for S = 1/2 two-leg Heisenberg ladders, for which results are presented.

High-order series expansion of non-Hermitian quantum spin models - Lenke, Lea; Mühlhauser, Matthias; Schmidt, Kai Phillip (Physical Review B, 2021)
We investigate the low-energy physics of non-Hermitian quantum spin models with PT symmetry. To this end, we consider the one-dimensional Ising chain and the two-dimensional toric code in a non-Hermitian staggered field. For both systems, dual descriptions in terms of non-Hermitian staggered Ising interactions in a conventional transverse field exist. We perform high-order series expansions about the high- and low-field limit for both systems to determine the ground-state energy per site and the one-particle gap. The one-dimensional non-Hermitian Ising chain is known to be exactly solvable. Its ground-state phase diagram consists of second-order quantum phase transitions, which can be characterized by logarithmic singularities of the second derivative of the ground-state energy and, in the symmetry-broken phase, the gap closing of the low-field gap. In contrast, the gap closing from the high-field phase is not accessible perturbatively due to the complex energy and the occurrence of exceptional lines in the high-field gap expression. For the two-dimensional toric code in a non-Hermitian staggered field, we study the quantum robustness of the topologically ordered phase by the gap closing of the low-field gap. We find that the well-known second-order quantum phase transition of the toric code in a uniform field extends into a large portion of the non-Hermitian parameter space. However, the series expansions become unreliable for a dominant anti-Hermitian field. Interestingly, the analysis of the high-field gap reveals the potential presence of an intermediate region.
CRIS-Team Scopus Importer:2021-12-17

Holst-MacDowell-Mansouri action for (extended) supergravity with boundaries and super Chern-Simons theory - Eder, Konstantin; Sahlmann, Hanno (Journal of High Energy Physics, 2021)
In this article, the Cartan geometric approach toward (extended) supergravity in the presence of boundaries will be discussed. In particular, based on new developments in this field, we will derive the Holst variant of the MacDowell-Mansouri action for N=1 and N=2 pure AdS supergravity in D=4 for arbitrary Barbero-Immirzi parameters. This action turns out to play a crucial role in context of boundaries in the framework of supergravity if one imposes supersymmetry invariance at the boundary. For the N=2 case, it follows that this amounts to the introduction of a θ-topological term to the Yang-Mills sector which explicitly depends on the Barbero-Immirzi parameter. This shows the close connection between this parameter and the θ-ambiguity of gauge theory. We will also discuss the chiral limit of the theory, which turns out to possess some very special properties such as the manifest invariance of the resulting action under an enlarged gauge symmetry. Moreover, we will show that demanding supersymmetry invariance at the boundary yields a unique boundary term corresponding to a super Chern-Simons theory with OSp(N|2) gauge group. In this context, we will also derive boundary conditions that couple boundary and bulk degrees of freedom and show equivalence to the results found in the D'Auria-Fré approach in context of the non-chiral theory. These results provide a step towards of quantum description of supersymmetric black holes in the framework of loop quantum gravit
Keywords: Supergravity Models; AdS-CFT Correspondence; Chern-Simons Theories

Horizon entropy with loop quantum gravity methods - Sahlmann, Hanno; Pranzetti, Daniele (Physics Letters B, 2015)
We show that the spherically symmetric isolated horizon can be described in terms of an SU(2) connection and an su(2)-valued one-form, obeying certain constraints. The horizon symplectic structure is precisely the one of 3d gravity in a first order formulation. We quantize the horizon degrees of freedom in the framework of loop quantum gravity, with methods recently developed for 3d gravity with non-vanishing cosmological constant. Bulk excitations ending on the horizon act very similarly to particles in 3d gravity. The Bekenstein-Hawking law is recovered in the limit of imaginary Barbero-Immirzi parameter. Alternative methods of quantization are also discussed.

Horizons and free-path distributions in quasiperiodic Lorentz gases - Kraemer, Ata; Schmiedeberg, Michael; Sanders, David (Physical Review E, 2015)
We study the structure of quasiperiodic Lorentz gases, i.e., particles bouncing elastically off fixed obstacles arranged in quasiperiodic lattices. By employing a construction to embed such structures into a higher-dimensional periodic hyperlattice, we give a simple and efficient algorithm for numerical simulation of the dynamics of these systems. This same construction shows that quasiperiodic Lorentz gases generically exhibit a regime with infinite horizon, that is, empty channels through which the particles move without colliding, when the obstacles are small enough; in this case, the distribution of free paths is asymptotically a power law with exponent -3, as expected from infinite-horizon periodic Lorentz gases. For the critical radius at which these channels disappear, however, a new regime with locally finite horizon arises, where this distribution has an unexpected exponent of -5, previously observed only in a Lorentz gas formed by superposing three incommensurable periodic lattices in the Boltzmann-Grad limit where the radius of the obstacles tends to zero.

Horizonte der Einsamkeit. Reinhard Jirgl im Dialog zu »Nichts von euch auf Erden« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

How antagonistic salts cause nematic ordering and behave like diblock copolymers - Jung, Wieland David Krischan; Rivas, Nicolas; Harting, Jens (Journal of Chemical Physics, 2019)
We present simulation results and an explanatory theory on how antagonistic salts affect the spinodal decomposition of binary fluid mixtures. We find that spinodal decomposition is arrested and complex structures form only when electrostatic ion-ion interactions are small. In this case, the fluid and ion concentrations couple and the charge field can be approximated as a polynomial function of the relative fluid concentrations alone. When the solvation energy associated with transferring an ion from one fluid phase to the other is of the order of a few kBT, the coupled fluid and charge fields evolve according to the Ohta-Kawasaki free energy functional. This allows us to accurately predict structure sizes and reduce the parameter space to two dimensionless numbers. The lamellar structures induced by the presence of the antagonistic salt in our simulations exhibit a high degree of nematic ordering and the growth of ordered domains over time follows a power law. This power law carries a time exponent proportional to the salt concentration. We qualitatively reproduce and interpret neutron scattering data from previous experiments of similar systems. The dissolution of structures at high salt concentrations observed in these experiments agrees with our simulations, and we explain it as the result of a vanishing surface tension due to electrostatic contributions. We conclude by presenting 3D results showing the same morphologies as predicted by the Ohta-Kawasaki model as a function of volume fraction and suggesting that our findings from 2D systems remain valid in 3D.
CRIS-Team WoS Importer:2019-03-06

Hybrid Loop Quantum Cosmology: An Overview - Elizaga de Navascués, Beatriz; Mena Marugan, Guillermo A. (Frontiers in Astronomy and Space Sciences, 2021)
Loop Quantum Gravity is a nonperturbative and background independent program for the quantization of General Relativity. Its underlying formalism has been applied successfully to the study of cosmological spacetimes, both to test the principles and techniques of the theory and to discuss its physical consequences. These applications have opened a new area of research known as Loop Quantum Cosmology. The hybrid approach addresses the quantization of cosmological systems that include fields. This proposal combines the description of a finite number of degrees of freedom using Loop Quantum Cosmology, typically corresponding to a homogeneous background, and a Fock quantization of the field content of the model. In this review we first present a summary of the foundations of homogeneous Loop Quantum Cosmology and we then revisit the hybrid quantization approach, applying it to the study of Gowdy spacetimes with linearly polarized gravitational waves on toroidal spatial sections, and to the analysis of cosmological perturbations in preinflationary and inflationary stages of the Universe. The main challenge is to extract predictions about quantum geometry effects that eventually might be confronted with cosmological observations. This is the first extensive review of the hybrid approach in the literature on Loop Quantum Cosmology.
CRIS-Team WoS Importer:2021-07-02

Hydrodynamic particle interactions in linear and radial viscosity gradients - Ziegler, Sebastian; Smith, Ana-Suncana (Journal of Fluid Mechanics, 2022)
We present a versatile perturbative calculation scheme to determine the leading-order correction to the mobility matrix for particles in a low-Reynolds-number fluid with spatially variant viscosity. To this end, we exploit the Lorentz reciprocal theorem and the reflection method in the far field approximation. To demonstrate how to apply the framework to a particular choice of a viscosity field, we first study particles in a finite-size, interface-like, linear viscosity gradient. The extent of the latter should be significantly larger than the particle separation. Both situations of symmetrically and asymmetrically placed particles within such an odd symmetric viscosity gradient are considered. As a result, long-range flow fields are identified that decay by one order slower than their constant-viscosity counterparts. Self-mobilities for particle rotations and translations are affected, while for asymmetric placement, additional correction appears for the latter. The mobility terms associated with hydrodynamic interactions between the particles also need to be corrected, in a placement-specific manner. While the results are derived for the system of two particles, they apply also to many-particle systems. Furthermore, we treat the viscosity gradients induced by two particles with temperatures different from that of the surrounding fluid. Assuming a linear relation between fluid temperature and viscosity, we find that both the self-mobilities of the particles as well as the mobility terms for hydrodynamic interactions increase for hot particles and decrease for cold particles.
CRIS-Team WoS Importer:2022-07-01

Immirzi parameter in quantum general relativity - Thiemann, Thomas; Rovelli, Carlo (Physical Review D, 1998)
Barbero has generalized the Ashtekar canonical transformation to a one-parameter scale transformation U(gamma) on the phase space of general relativity. Immirzi has noticed that in loop quantum gravity this transformation alters the spectra of geometrical quantities. We show that U(gamma) is a canonical transformation that cannot be implemented unitarily in quantum theory. This implies that there exists a one-parameter quantization ambiguity in quantum gravity, namely, a free parameter that enters the construction of the quantum theory. The purpose of this paper is to elucidate the origin and the role of this free parameter.

Impact of Electron Solvation on Ice Structures at the Molecular Scale - Bertram, Cord; Auburger, Philipp; Bockstedte, Michel Georg; Staebler, Julia; Bovensiepen, Uwe; Morgenstern, Karina (Journal of Physical Chemistry Letters, 2020)
Electron attachment and solvation at ice structures are well-known phenomena. The energy liberated in such events is commonly understood to cause temporary changes at such ice structures, but it may also trigger permanent modifications to a yet unknown extent. We determine the impact of electron solvation on D2O structures adsorbed on Cu(111) with low-temperature scanning tunneling microscopy, two-photon photoemission, and ab initio theory. Solvated electrons, generated by ultraviolet photons, lead not only to transient but also to permanent structural changes through the rearrangement of individual molecules. The persistent changes occur near sites with a high density of dangling OD groups that facilitate electron solvation. We conclude that energy dissipation during solvation triggers permanent molecular rearrangement via vibrational excitation.
CRIS-Team Scopus Importer:2020-03-13

Implications from Different Regularisations for the Canonically Quantised k=1 FLRW Spacetime - Weigl, Stefan; Giesel, Kristina; Liegener, Klaus (2018)
In this work we present the regularisation of the Hamiltonian constraints in the context of the canonical description of general relativity (GR). We will start with the Hamiltonian formulation of GR and then introduce the Ashtekar-Barbero variables. After investigating the gauge trans- formations generated by the Hamiltonian constraints we present the holonomy-flux algebra where we also regularise the constraints. We will give a full derivation of the FLRW metric and then conclusively perform a regularisation for k=1 on spherical graphs.

Importance of d-p Coulomb interaction for high T-C cuprates and other oxides - Hansmann, Philipp; Parragh, N.; Toschi, Alessandro; Sangiovanni, Giorgio; Held, Karsten (New Journal of Physics, 2014)
Current theoretical studies of electronic correlations in transition metal oxides typically only account for the local repulsion between d-electrons even if oxygen ligand p-states are an explicit part of the effective Hamiltonian. Interatomic interactions such as U-pd between d- and (ligand) p-electrons, as well as the local interaction between p-electrons, are neglected. Often, the relative d-p orbital splitting has to be adjusted 'ad hoc' on the basis of the experimental evidence. By applying the merger of local density approximation and dynamical mean field theory to the prototypical case of the three-band Emery dp model for the cuprates, we demonstrate that, without any 'ad hoc' adjustment of the orbital splitting, the charge transfer insulating state is stabilized by the interatomic interaction U-pd. Our study hence shows how to improve realistic material calculations that explicitly include the p-orbitals.
CRIS-Team WoS Importer:2020-02-19

Improved effective dynamics of loop-quantum-gravity black hole and Nariai limit - Han, Muxin; Liu, Hongguang (Classical and Quantum Gravity, 2022)
We propose a new model of the spherical symmetric quantum black hole in the reduced phase space formulation. We deparametrize gravity by coupling to the Gaussian dust which provides the material coordinates. The foliation by dust coordinates covers both the interior and exterior of the black hole. After the spherical symmetry reduction, our model is a 1 + 1 dimensional field theory containing infinitely many degrees of freedom. The effective dynamics of the quantum black hole is generated by an improved physical Hamiltonian H-Delta. The holonomy correction in H-Delta is implemented by the (mu) over bar -scheme regularization with a Planckian area scale Delta (which often chosen as the minimal area gap in loop quantum gravity). The effective dynamics recovers the semiclassical Schwarzschild geometry at low curvature regime and resolves the black hole singularity with Planckian curvature, e.g. R mu nu rho sigma R mu nu rho sigma similar to 1/Delta(2). Our model predicts that the evolution of the black hole at late time reaches the charged Nariai geometry dS(2) x S-2 with Planckian radii similar to root Delta. The Nariai geometry is stable under linear perturbations but may be unstable by nonperturbative quantum effects. Our model suggests the existence of quantum tunneling of the Nariai geometry and a scenario of black-hole-to-white-hole transition.
CRIS-Team WoS Importer:2022-01-28

Improved (mu)over-bar-scheme effective dynamics of full loop quantum gravity - Han, Muxin; Liu, Hongguang (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2020)
We propose a new derivation from full loop quantum gravity (LQG) to the loop quantum cosmology improved (mu) over bar -scheme effective dynamics, based on the reduced phase-space formulation of LQG and a proposal of an effective Hamiltonian/action in full LQG. A key step of our program is an improved regularization of full LQG Hamiltonian on a cubic lattice. The improved Hamiltonian uses a set of "dressed holonomies" h(Delta) (s) which depend on both the connection A and the length of the curve s. With the improved Hamiltonian, we propose a quantum effective action and derive a new set of effective equations of motion (EOMs) for full LQG. Then, we show that these new EOMs imply the (mu) over bar -scheme effective dynamics for both the homogeneous-isotropic and Bianchi-I cosmologies, and predict a bounce and Planckian critical density. As a byproduct, although the model is defined on a cubic lattice, we find that the improved effective Hamiltonian of cosmology is invariant under lattice refinement. The cosmological effective dynamics, predictions for the bounce, and critical density are results in the continuum limit.
CRIS-Team WoS Importer:2020-10-09

Improving the Performance of Supported Ionic Liquid Phase Catalysts for the Ultra-Low-Temperature Water Gas Shift Reaction Using Organic Salt Additives - Wolf, Patrick; Wick, Christian; Mehler, Julian; Blaumeiser, Dominik; Schötz, Simon; Bauer, Tanja; Libuda, Jörg; Smith, David; Smith, Ana-Suncana; Haumann, Marco (ACS Catalysis, 2022)
The water gas shift reaction (WGSR) is catalyzed by supported ionic liquid phase (SILP) systems containing homogeneous Ru complexes dissolved in ionic liquids (ILs). These systems work at very low temperatures, that is, between 120 and 160 °C, as compared to >200 °C in the conventional process. To improve the performance of this ultra-low-temperature catalysis, we investigated the influence of various additives on the catalytic activity of these SILP systems. In particular, the application of methylene blue (MB) as an additive doubled the activity. Infrared spectroscopy measurements combined with density functional theory (DFT) calculations excluded a coordinative interaction of MB with the Ru complex. In contrast, state-of-the-art theoretical calculations elucidated the catalytic effect of the additives by non-covalent interactions. In particular, the additives can significantly lower the barrier of the rate-determining step of the reaction mechanism via formation of hydrogen bonds. The theoretical predictions, thereby, showed excellent agreement with the increase of experimental activity upon variation of the hydrogen bonding moieties in the additives investigated.
CRIS-Team Scopus Importer:2022-06-03
Keywords: electronic interaction; methylene blue; ruthenium; supported ionic liquid phase; water gas shift reaction

Improving the performance of supported ionic liquid phase (SILP) catalysts for the ultra-low-temperature water-gas shift reaction using metal salt additives - Wolf, Patrick; Aubermann, Manfred; Wolf, Moritz; Bauer, Tanja; Blaumeiser, Dominik; Stepic, Robert; Wick, Christian; Smith, David M.; Smith, Ana-Suncana; Wasserscheid, Peter; Libuda, Jörg; Haumann, Marco (Green Chemistry, 2019)
Supported ionic liquid phase (SILP) catalyst systems containing homogeneous Ru complexes dissolved in ionic liquids (ILs) catalyze the water-gas shift reaction (WGSR) at very low temperatures, i.e., between 120 and 160 °C. One limiting factor of the SILP WGS technology is the low solubility of CO in most ILs. To overcome this issue, we study the influence of different transition metal chloride additives on the activity of Ru-based WGS SILP catalysts. CuCl as the additive was found to enhance the activity by almost 30%. This increase in activity peaks at a CuCl addition of 4 M as a result of the interplay between the increasing CO uptake in the ionic liquid film as evidenced by means of CO sorption and thermogravimetry, and the increasing, unfavorable ionic liquid acidity at too high CuCl concentrations. The respective chlorocuprate species were identified by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with density functional theory (DFT) calculations. We attribute the enhanced catalytic performance to cuprate ions that act as CO shuttles within the ionic liquid film.
CRIS-Team Scopus Importer:2019-09-27

Individual Tracer Atoms in an Ultracold Dilute Gas - Hohmann, Michael; Kindermann, Farina; Lausch, Tobias; Mayer, Daniel; Schmidt, Felix; Lutz, Eric; Widera, Artur (Physical Review Letters, 2017)
We report on the experimental investigation of individual Cs atoms impinging on a dilute cloud of ultracold Rb atoms with variable density. We study the relaxation of the initial nonthermal state and detect the effect of single collisions which has so far eluded observation. We show that, after few collisions, the measured spatial distribution of the tracer atoms is correctly described by a Langevin equation with a velocity-dependent friction coefficient, over a large range of Knudsen numbers. Our results extend the simple and effective Langevin treatment to the realm of light particles in dilute gases. The experimental technique developed opens up the microscopic exploration of a novel regime of diffusion at the level of individual collisions.
CRIS-Team Scopus Importer:2023-03-27

Inequivalent Routes across the Mott Transition in V2O3 Explored by X-Ray Absorption - Rodolakis, Fanny; Hansmann, Philipp; Rueff, J. -P.; Toschi, Alessandro; Haverkort, M. W.; Sangiovanni, Giorgio; Tanaka, A.; Saha-Dasgupta, T.; Andersen, O. K.; Held, Karsten; Sikora, Marcin; Alliot, I.; et al. (Physical Review Letters, 2010)
The changes in the electronic structure of V2O3 across the metal-insulator transition induced by temperature, doping, and pressure are identified using high resolution x-ray absorption spectroscopy at the V pre-K edge. Contrary to what has been taken for granted so far, the metallic phase reached under pressure is shown to differ from the one obtained by changing doping or temperature. Using a novel computational scheme, we relate this effect to the role and occupancy of the a(1g) orbitals. This finding unveils the inequivalence of different routes across the Mott transition in V2O3.
CRIS-Team WoS Importer:2020-02-19

Inferring spatial organization of bonds within adhesion clusters by exploiting fluctuations of soft interfaces - Smith, Ana-Suncana; Fenz, S. F.; Sengupta, Kheya (EPL - Europhysics Letters, 2010)
Detecting the organization of bonds within adhesion domains connecting two interacting membranes is, at present, extremely challenging. Herein we present a technique, based on Reflection Interference Contrast Microscopy, which uses spontaneous thermal fluctuations of a soft interface as a tool to identify the organization of specific ligand-receptor bonds. The key is a time-resolved analysis of micro-interferometric data that systematically quantifies fluctuations and enables the detection of their suppression due to the formation of bonds, which, in turn, allows the identification of the bond organization without the use of fluorescent labelling. The identification of a new type of bond organization characterized by sparsely distributed bonds, as well as detection of pinning centres of nanometric size is presented. Copyright (C) EPLA, 2010
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; MULTICOMPONENT MEMBRANES; PHASE-SEPARATION; DIFFUSION

Inflammatory activation of the FcγR and IFNγR pathways co-influences the differentiation and activity of osteoclasts - Grötsch, Bettina; Schachtschabel, Elisabeth; Tripal, Philipp; Schmid, Benjamin; Smith, Ana-Suncana; Schett, Georg; Bozec, Aline (Frontiers in Immunology, 2022)
Osteoclasts are polykaryons formed by cell–cell fusion of highly motile progenitors of the myeloid lineage. Osteoclast activity can preserve skeletal strength and bone homeostasis. However, osteoclasts are responsible for bone destruction in rheumatoid arthritis (RA). Fc receptors activated by IgG immune complexes (IC) can boost osteoclast differentiation and bone loss in the course of RA. In contrast, interferon (IFN) γ secreted by immune cells blocks osteoclast activation. Despite their hypothetical importance in the regulation of osteoclast differentiation in RA, the interconnection between the two pathways has not been described so far. Here, we show by total internal reflection fluorescence (TIRF) microscopy that FcγR3 and IFNγ receptor (IFNγR) locate at close vicinity to each other on the human osteoclast surface. Moreover, the average distance increases during the differentiation process. Interestingly, FcγR and IFNγR activation shapes the position of both receptors to each other. Surprisingly, the inhibitory action of IFNγ on in-vitro human osteoclast differentiation depends on the osteoclast differentiation stage. Indeed, IFNγR activation in early osteoclast precursors completely inhibits the formation of polynucleated osteoclasts, while in premature osteoclasts, it further enhanced their fusion. In addition, gene expression analyses showed that IFNγR activation on early precursor cells but not on premature osteoclasts could induce FcγR expression, suggesting a co-regulation of both receptors on human osteoclast precursors. Phosphokinase array data of precursor cells demonstrate that the observed divergence of IFNγR signaling is dependent on the mitogen−activated protein kinase (MAPK) downstream signaling pathway. Overall, our data indicate that FcγR and IFNγR signaling pathways co-influence the differentiation and activity of osteoclasts dependent on the differentiation state, which might reflect the different stages in RA.
CRIS-Team Scopus Importer:2022-10-07
Keywords: FcγR3; IFNγR; IFNγR signaling; ITAM signaling; Osteoclast; rheumatoid arthritis (RA)

Inhomogeneous disordering at a photoinduced charge density wave transition - Picano, Antonio; Grandi, Francesco; Eckstein, Martin (Physical Review B, 2023)
Using ultrashort laser pulses, it has become possible to probe the dynamics of long-range order in solids on microscopic timescales. In the conventional description of symmetry-broken phases within time-dependent Ginzburg-Landau theory, the order parameter evolves coherently, with small fluctuations along an average trajectory. Recent experiments, however, indicate that some systems can support a different scenario, named ultrafast inhomogeneous disordering, where the average order parameter is no longer representative of the state on the atomic scale. Here we theoretically show that ultrafast disordering can occur in a minimal, yet paradigmatic, model for a Peierls instability if atomic scale inhomogeneities of both the electronic structure and the charge density wave order parameter are taken into account. The latter is achieved using a nonequilibrium generalization of statistical dynamical mean-field theory coupled to stochastic differential equations for the order parameter.
CRIS-Team Scopus Importer:2023-06-30

Input polarization-independent polarization-sensitive optical coherence tomography using a depolarizer - Sharma, Shivani; Hartl, Georg; Naveed, Sheeza K.; Blessing, Katharina; Sharma, Gargi; Singh, Kanwarpal (Review of Scientific Instruments, 2020)
Polarization-sensitive optical coherence tomography is gaining attention because of its ability to diagnose certain pathological conditions at an early stage. The majority of polarization-sensitive optical coherence tomography systems require a polarization controller and a polarizer to obtain the optimal polarization state of the light at the sample. Such systems are prone to misalignment since any movement of the optical fiber normally coupled to the light source will change the polarization state of the incident beam. We propose and demonstrate an input polarization-independent polarization-sensitive optical coherence tomography system using a depolarizer that works for any input polarization state of the light source. The change in the optical power at the sample for arbitrary input polarized light for the standard polarization-sensitive optical coherence tomography system was found to be approximately 84% compared to 9% for our proposed method. The developed system was used to measure the retardance and optical axis orientation of a quarter-wave plate and the obtained values matched closely to the expectation. To further demonstrate the capability of measuring the birefringent properties of biological samples, we also imaged the nail bed. We believe that the proposed system is a robust polarization-sensitive optical coherence tomography system and that it will improve the diagnostic capabilities in clinical settings.
CRIS-Team Scopus Importer:2020-04-24

Insights from molecular dynamics simulations on structural organization and diffusive dynamics of an ionic liquid at solid and vacuum interfaces - Vučemilović-Alagić, Nataša; Banhatti, Radha D.; Stepic, Robert; Wick, Christian; Berger, Daniel; Gaimann, Mario U.; Baer, Andreas; Harting, Jens; Smith, David M.; Smith, Ana-Suncana (Journal of Colloid and Interface Science, 2019)
Hypothesis: A reliable modelling approach is required for simultaneous characterisation of static and dynamic properties of bulk and interfacial ionic liquids (ILs). This is a prerequisite for a successful investigation of experimentally inaccessible, yet important properties, including those that change significantly with the distance from both vacuum and solid interfaces. Simulations: We perform molecular dynamics simulations of bulk [C2Mim][NTf2], and thick IL films in contact with vacuum and hydroxylated sapphire surface, using the charge methods CHelpG, RESP-HF and RESP-B3LYP with charge scaling factors 1.0, 0.9 and 0.85. Findings: By determining and employing appropriate system sizes and simulations lengths, and by benchmarking against self-diffusion coefficients, surface tension, X-ray reflectivity, and structural data, we identify RESP-HF/0.9 as the best non-polarizable force field for this IL. We use this optimal parametrisation to predict novel physical properties of confined IL films. First we fully characterise the internal configurations and orientations of IL molecules relative to, and as a function of the distance from the solid and vacuum interfaces. Second, we evaluate densities together with mobilities in-plane and normal to the interfaces and find that strong correlations between the IL's stratification and diffusive transport in the interfacial layers persist for several nanometres deep into IL films.
CRIS-Team Scopus Importer:2019-06-21
Keywords: Interfaces; Ionic liquid; Lateral diffusion; Molecular dynamics simulation; Nano-scale film; Non-polarizable force field; Residence time; Sampling; Sapphire substrate; Structural order; Surface tension; X-Ray reflectivity

In situ tunable nonlinearity and competing signal paths in coupled superconducting resonators - Fischer, Michael; Chen, Qi Ming; Besson, Christian; Eder, Peter; Goetz, Jan; Pogorzalek, Stefan; Renger, Michael; Xie, Edwar; Hartmann, Michael; Fedorov, Kirill G.; Marx, Achim; Deppe, Frank; et al. (Physical Review B, 2021)
We have fabricated and studied a system of two tunable and coupled nonlinear superconducting resonators. The nonlinearity is introduced by galvanically coupled dc superconducting quantum interference devices. We simulate the system response by means of a circuit model, which includes an additional signal path introduced by the electromagnetic environment. Furthermore, we present two methods allowing us to experimentally determine the nonlinearity. First, we fit the measured frequency and flux dependence of the transmission data to simulations based on the equivalent circuit model. Second, we fit the power dependence of the transmission data to a model that is predicted by the nonlinear equation of motion describing the system. Our results show that we are able to tune the nonlinearity of the resonators by almost two orders of magnitude via an external coil and two on-chip antennas. The studied system represents a basic building block for larger systems, allowing for quantum simulations of bosonic many-body systems with a larger number of lattice sites.
CRIS-Team Scopus Importer:2021-04-16

Integral geometry in statistical physics - Mecke, Klaus (1998)
(C) Morphological measures are a novel method for the description of complex spatial structures aiming for relevant order parameters and structure information complement to correlation functions. Typical applications address Turing patterns in chemical reaction diffusion systems, homogeneous phases evolving during spinodal decomposition, and the distribution of galaxies and clusters of galaxies in the Universe as a prominent example of a point process in nature.

Interaction of topological states of sounds and light with solid-state emitters as a quantum hybrid platform - Lemonde, Marc Antoine; Peano, Vittorio; Rabl, Peter; Angelakis, Dimitris D. (Optics InfoBase Conference Papers, 2019)
A large set of physically different platforms are still in the race, as promising quantum systems, to perform efficient quantum information processing. Each of them offer particular figures of merit and weaknesses. An important paradigm for quantum computation is to consider hybrid systems where the strengths of different systems can be harvested while mitigating their weaknesses [1]. Meanwhile, increasing efforts are being devoted to topological phases of matter in bosonic systems to perform robust manipulation of quantum information, where topologically protected edge states can be utilized as quantum channels [2].
CRIS-Team Scopus Importer:2021-04-20

Inter-membrane adhesion mediated by mobile linkers: Effect of receptor shortage - Fenz, Susanne F.; Smith, Ana-Suncana; Merkel, Rudolf; Sengupta, Kheya (Soft Matter, 2011)
Giant unilamellar vesicles (GUVs) adhering to supported bilayers were used as a model system to mimic ligand-receptor mediated cell-cell adhesion. We present the effect of varying the concentration of receptors (neutravidin on the bilayer) and ligands (biotin on the vesicle) on GUV adhesion and the organization of receptors in the adhesion zone. At high concentrations of both ligands and receptors, the adhesion is strong, all the available membrane is adhered and receptors are accumulated under the adhered membrane up to the geometrical limit of close packing. At low concentrations of receptors (<0.5%), and an arbitrary concentration of ligands (>= 0.1%), adhesion does not proceed to completion: the membrane is only partially bound and parts of it still fluctuate. The receptors tend to accumulate under the adhered membrane but the filling is partial. Receptors get jammed and form clusters with fractal like shapes along the rim of the adhered vesicle in such a way that the annular cluster prevents further filling of the adhesion disc. We characterize the filling in terms of a compaction factor and the final concentration. Interestingly, the closing of the ring of jammed clusters switches the interior of the adhesion disc from one thermodynamic ensemble to another. In the new ensemble the receptors sealed within the adhesion disc are mobile but their number is fixed. Under such conditions, the usually strong neutravidin/biotin bond is weak. The incomplete adhesion state can be attributed to a combination of the effects of diffusion, jamming and the competition of enthalpy and entropy on bond formation. The formation of jammed receptor clusters reported here represents a new mechanism that influences membrane adhesion.
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; VESICLE ADHESION; DYNAMICS; SURFACE; BOND; STREPTAVIDIN; GLYCOPROTEIN; TRANSITION; DIFFUSION

Intermolecular Singlet Fission in Unsymmetrical Derivatives of Pentacene in Solution - Casillas Pacheco, Ruben; Adam, Matthias; Brana Coto, Pedro; Waterloo, Andreas; Zirzlmeier, Johannes; Reddy, Seelam Rajagopala; Hampel, Frank; Mcdonald, Robert; Tykwinski, Rik R.; Thoss, Michael; Guldi, Dirk Michael (Advanced Energy Materials, 2019)
Intermolecular singlet fission (SF) is an electronically coupled process between two chromophores, where distance dependences are decisive in terms of rates and yields. In the current work, a family of pentacene derivatives featuring different functional groups have been designed, synthesized, and probed with respect to intermolecular SF in the low, medium, and high concentration regimes rather than in the solid state. By means of advanced photophysical techniques, global analysis modeling, and ab initio calculations, a model for intermolecular SF is postulated. The model is based on an early key intermediate, which involves the diffusional encounter between one pentacene in its singlet excited-state with another one in its ground state and which features excimer characteristics. This is followed by a transformation into a coupled triplet excited-state. The role of the functional group appended to pentacene is analyzed with respect to steric shielding of the pentacene core as a means to prevent photophysical degradation, as well as control diffusional encounter and, subsequently, SF. The findings demonstrate the potential of new molecular materials for SF, especially in solution studies, as well as the challenges of implementing them in energy conversion schemes due to the appearance of photodegradation processes that compete with SF.
CRIS-Team WoS Importer:2019-02-21

Interorbital singlet pairing in Sr2RuO4: A Hund's superconductor - Käser, Stefan; Strand, Hugo U.R.; Wentzell, Nils; Georges, Antoine; Parcollet, Olivier; Hansmann, Philipp (Physical Review B, 2022)
We study the superconducting gap function of Sr2RuO4. By solving the linearized Eliashberg equation with a correlated pairing vertex extracted from a dynamical mean-field calculation we identify the dominant pairing channels. An analysis of the candidate gap functions in orbital and quasiparticle band basis reveals that an interorbital singlet pairing of even parity is in agreement with experimental observations. It reconciles in particular the occurrence of a two-component order parameter with the presence of line nodes of quasiparticles along the c axis in the superconducting phase. The strong angular dependence of the gap along the Fermi surface is in stark contrast to its quasilocality when expressed in the orbital basis. We identify local interorbital spin correlations as the driving force for the pairing and thus reveal the continuation of Hund's physics into the superconducting phase.
CRIS-Team Scopus Importer:2022-04-29

Intracavity Squeezing Can Enhance Quantum-Limited Optomechanical Position Detection through Deamplification - Peano, Vittorio; Schwefel, Harald; Marquardt, Christoph; Marquardt, Florian (Physical Review Letters, 2015)
It has been predicted and experimentally demonstrated that by injecting squeezed light into an optomechanical device, it is possible to enhance the precision of a position measurement. Here, we present a fundamentally different approach where the squeezing is created directly inside the cavity by a nonlinear medium. Counterintuitively, the enhancement of the signal-to-noise ratio works by deamplifying precisely the quadrature that is sensitive to the mechanical motion without losing quantum information. This enhancement works for systems with a weak optomechanical coupling and/or strong mechanical damping. This can allow for larger mechanical bandwidth of quantum-limited detectors based on optomechanical devices. Our approach can be straightforwardly extended to quantum nondemolition qubit detection.
CRIS-Team Scopus Importer:2022-06-05

Introduction - Heydenreich, Aura; Mecke, Klaus (Physics and Literature. Concepts – Transfer – Aestheticization, 2021)

Introduction to Dirac observables - Giesel, Kristina (International Journal of Modern Physics A, 2008)
We give a brief introduction to Dirac observables and review the general construction of such Dirac observables for constrained systems in the framework of the Relational Formalism introduced by Rovelli(1) and further mathematically developed by Dittrich.(2) Finally we birefly discuss appropriate clocks for General Relativity and the evolution of observables generated by a so called physical Hamiltonian.

Investigation of inverse design of multilayer thin-films with conditional invertible neural networks - Luce, Alexander; Mahdavi, Ali; Wankerl, Heribert; Marquardt, Florian (Machine Learning: Science and Technology, 2023)
In this work, we apply conditional invertible neural networks (cINN) to inversely design multilayer thin-films given an optical target in order to overcome limitations of state-of-the-art optimization approaches. Usually, state-of-the-art algorithms depend on a set of carefully chosen initial thin-film parameters or employ neural networks which must be retrained for every new application. We aim to overcome those limitations by training the cINN to learn the loss landscape of all thin-film configurations within a training dataset. We show that cINNs can generate a stochastic ensemble of proposals for thin-film configurations that are reasonably close to the desired target depending only on random variables. By refining the proposed configurations further by a local optimization, we show that the generated thin-films reach the target with significantly greater precision than comparable state-of-the-art approaches. Furthermore, we tested the generative capabilities on samples which are outside of the training data distribution and found that the cINN was able to predict thin-films for out-of-distribution targets, too. The results suggest that in order to improve the generative design of thin-films, it is instructive to use established and new machine learning methods in conjunction in order to obtain the most favorable results.
CRIS-Team Scopus Importer:2023-03-03
Keywords: conditional invertible neural networks; global optimization; inverse design; latent space; multilayer thin-films

Irreducibility of the Ashtekar-Isham-Lewandowski representation - Sahlmann, Hanno; Thiemann, Thomas (Classical and Quantum Gravity, 2006)
Much of the work in loop quantum gravity and quantum geometry rests on a mathematically rigorous integration theory on spaces of distributional connections. Most notably, a diffeomorphism invariant representation of the algebra of basic observables of the theory, the Ashtekar-Isham-Lewandowski (AIL) representation, has been constructed. Recently, several uniqueness results for this representation have been worked out. In the present paper, we contribute to these efforts by showing that the AIL representation is irreducible, provided it is viewed as the representation of a certain C*-algebra which is very similar to the Weyl algebra used in the canonical quantization of free quantum field theories. © 2006 IOP Publishing Ltd.

Ising anyons with a string tension - Schulz, Marc Daniel; Dusuel, Sebastien; Misguich, Gregoire; Schmidt, Kai Phillip; Vidal, Julien (Physical Review B, 2014)
We consider the string-net model on the honeycomb lattice for Ising anyons in the presence of a string tension. This competing term induces a nontrivial dynamics of the non-Abelian anyonic quasiparticles and may lead to a breakdown of the topological phase. Using high-order series expansions and exact diagonalizations, we determine the robustness of this doubled Ising phase, which is found to be separated from two gapped phases. An effective quantum dimer model emerges in the large tension limit, giving rise to two different translation symmetry-broken phases. Consequently, we obtain four transition points, two of which are associated with first-order transitions whereas the two others are found to be continuous and provide examples of recently proposed Bose condensation for anyons.

Ising model in a light-induced quantized transverse field - Rohn, Jonas; Hörmann, Max; Genes, Claudiu; Schmidt, Kai Phillip (Physical Review Research, 2020)
We investigate the influence of light-matter interactions on correlated quantum matter by studying the paradigmatic Dicke-Ising model. This type of coupling to a confined, spatially delocalized bosonic light mode, such as provided by an optical resonator, resembles a quantized transverse magnetic field of tunable strength. As a consequence, the symmetry-broken magnetic state breaks down for strong enough light-matter interactions to a paramagnetic state. The nonlocal character of the bosonic mode can change the quantum phase transition in a drastic manner, which we analyze quantitatively for the simplest case of the Dicke-Ising chain geometry. The results show a direct transition between a magnetically ordered phase with zero photon density and a magnetically polarized phase with superradiant behavior of the light. Our predictions are equally valid for the dual quantized Ising chain in a conventional transverse magnetic field.
CRIS-Team WoS Importer:2021-01-22

Jammed spheres: Minkowski tensors reveal onset of local crystallinity - Kapfer, Sebastian; Mickel, Walter; Mecke, Klaus; Schröder-Turk, Gerd (Physical Review E, 2012)
The local structure of disordered jammed packings of monodisperse spheres without friction, generated by the Lubachevsky-Stillinger algorithm, is studied for packing fractions above and below 64%. The structural similarity of the particle environments to fcc or hcp crystalline packings (local crystallinity) is quantified by order metrics based on rank-four Minkowski tensors. We find a critical packing fraction phi(c) approximate to 0.649, distinctly higher than previously reported values for the contested random close packing limit. At phi(c), the probability of finding local crystalline configurations first becomes finite and, for larger packing fractions, increases by several orders of magnitude. This provides quantitative evidence of an abrupt onset of local crystallinity at phi(c). We demonstrate that the identification of local crystallinity by the frequently used local bond-orientational order metric q(6) produces false positives and thus conceals the abrupt onset of local crystallinity. Since the critical packing fraction is significantly above results from mean-field analysis of the mechanical contacts for frictionless spheres, it is suggested that dynamic arrest due to isostaticity and the alleged geometric phase transition in the Edwards framework may be disconnected phenomena.

Kanonische Formulierung der Gravitationstheorien - Davygora, Yuriy; Thiemann, Thomas (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2009)

Kinematical Hilbert spaces for fermionic and Higgs quantum field theories - Thiemann, Thomas (Classical and Quantum Gravity, 1998)
Most of the fermionic part of this work is independent of the recent preprint by Baez and Krasnov and earlier work by Rovelli and Morales-Tecotl because we use new canonical fermionic variables, so-called Grassman-valued half-densities, which enable us to solve the difficult fermionic adjointness relations.

Kinematics of arbitrary spin matter fields in loop quantum gravity - Mansuroglu, Refik; Sahlmann, Hanno (Physical Review D, 2021)
Loop quantum gravity envisions a small scale structure of spacetime that is markedly different from that of the classical spacetime continuum. This has ramifications for the excitation of matter fields and for their coupling to gravity. There is a general understanding of how to formulate scalar fields, spin 12 fields, and gauge fields in the framework of loop quantum gravity. The goal of the present work is to investigate kinematical aspects of this coupling. We will study implications of the Gauß and diffeomorphism constraints for the quantum theory: We define and study a less ambiguous variant of the Baez-Krasnov path observables, and we investigate symmetry properties of spin network states imposed by diffeomorphism group averaging. We will do this in a setting which allows for matter excitations of spin 12 and higher. In the case of spin 12, we will also discuss extensions of it by introducing an electromagnetic field and antiparticles. We finally discuss how far the picture with matter excitations of higher spin can be obtained from classical actions for higher spin fields.
CRIS-Team Scopus Importer:2021-05-28

Kinetics of many-body reservoir engineering - Ribeiro, Hugo; Marquardt, Florian (Physical Review Research, 2020)
Recent advances illustrate the power of reservoir engineering in applications to many-body systems, such as quantum simulators based on superconducting circuits. We present a framework based on kinetic equations and noise spectra that can be used to understand both the transient and long-time dynamics of many particles coupled to an engineered reservoir in a number-conserving way. For the example of a bosonic array, we show that the nonequilibrium steady state can be expressed, in a wide parameter regime, in terms of a modified Bose-Einstein distribution with an energy-dependent temperature.
CRIS-Team WoS Importer:2021-01-22

Kitaev model and dimer coverings on the honeycomb lattice - Kamfor, Michael; Dusuel, Sebastien; Vidal, Julien; Schmidt, Kai Phillip (Journal of Statistical Mechanics-Theory and Experiment, 2010)
We consider an extension of the Kitaev honeycomb model based on arbitrary dimer coverings satisfying matching rules. We focus on three different dimer coverings having the smallest unit cells for which we calculate the ground-state phase diagram. We also study one- and two-vortex properties for these coverings in the Abelian phases and show that vortex-vortex interactions can be attractive or repulsive. These qualitative differences are confirmed analytically by high-order perturbative expansions around the isolated-dimer limit. Similarities and differences with the original Kitaev honeycomb model are discussed.
Keywords: solvable lattice models; frustrated systems (theory); spin liquids (theory); quantum phase transitions (theory)

Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: A systematic study - Matsushita, Y-I; Madjarova, Galia; Dewhurst, J. K.; Shallcross, Sam; Felser, Claudia; Sharma, Sangeeta; Gross, E. K. U. (Journal of Physics D: Applied Physics, 2017)
With a view to the design of hard magnets without rare earths we explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion. We consider the Heusler compounds Fe2YZ with Y = (Ni, Co, Pt), and Co2YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co2NiZ, Co2PtZ, and Fe2PtZ families the cubic phase is always, at T = 0, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe2NiZ and Fe2CoZ families this is the case for only 2 compounds - Fe2NiGe and Fe2NiSn. For all compounds in which a tetragonal distortion occurs we calculate the magnetocrystalline anisotropy energy (MAE) finding remarkably large values for the Pt containing Heuslers, but also large values for a number of the other compounds (e.g. Co2NiGa has an MAE of -2.38 MJ m-3). The tendency to a tetragonal distortion we find to be strongly correlated with a high density of states (DOS) at the Fermi level in the cubic phase. As a corollary to this fact we observe that upon doping compounds for which the cubic structure is stable such that the Fermi level enters a region of high DOS, a tetragonal distortion is induced and a correspondingly large value of the MAE is then observed.
CRIS-Team Scopus Importer:2022-04-14
Keywords: ab initio calculations; Heusler compunds; tetragonal distortion

Laser-nucleus interactions in the sudden regime - Kobzak, Sergei; Weidenmüller, Hans A.; Pálffy, Adriana (Physical Review C - Nuclear Physics, 2021)
The interaction between medium-weight nuclei and a strong zeptosecond laser pulse of MeV photons is investigated theoretically. Multiple absorption of photons competes with nuclear equilibration. We investigate the sudden regime. Here the rate of photon absorption is so strong that there is no time for the nucleus to fully equilibrate after each photon absorption process. We follow the temporal evolution of the system in terms of a set of rate equations. These account for dipole absorption and induced dipole emission, equilibration (modeled in terms of particle-hole states coupled by the residual nuclear interaction), and neutron decay (populating a chain of proton-rich nuclei). Our results are compared with earlier work addressing the adiabatic regime where equilibration is instantaneous. We predict the degree of excitation and the range of nuclei reached by neutron evaporation. These findings are relevant for planning future experiments.
CRIS-Team Scopus Importer:2021-05-21

Lattice Boltzmann simulations of the bead-spring microswimmer with a responsive stroke-from an individual to swarms - Pickl, Kristina; Pande, Jayant; Köstler, Harald; Rüde, Ulrich; Smith, Ana-Suncana (Journal of Physics: Condensed Matter, 2017)
Propulsion at low Reynolds numbers is often studied by defining artificial microswimmers which exhibit a particular stroke. The disadvantage of such an approach is that the stroke does not adjust to the environment, in particular the fluid flow, which can diminish the effect of hydrodynamic interactions. To overcome this limitation, we simulate a microswimmer consisting of three beads connected by springs and dampers, using the self-developed waLBerla and pe framework based on the lattice Boltzmann method and the discrete element method. In our approach, the swimming stroke of a swimmer emerges as a balance of the drag, the driving and the elastic internal forces. We validate the simulations by comparing the obtained swimming velocity to the velocity found analytically using a perturbative method where the bead oscillations are taken to be small. Including higher-order terms in the hydrodynamic interactions between the beads improves the agreement to the simulations in parts of the parameter space. Encouraged by the agreement between the theory and the simulations and aided by the massively parallel capabilities of the waLBerla-pe framework, we simulate more than ten thousand such swimmers together, thus presenting the first fully resolved simulations of large swarms with active responsive components.
Keywords: microswimming; three-sphere swimmer; lattice Boltzmann method; many-swimmer swarms; perturbation theory; Rotne-Prager theory

Lattice Boltzmann Simulations of Two Linear Microswimmers Using the Immersed Boundary Method - Geyer, D.; Ziegler, Sebastian; Sukhov, A.; Hubert, Maxime; Smith, Ana-Suncana; Aouane, O.; Malgaretti, P.; Harting, J. (Communications in Computational Physics, 2023)
The performance of a single or the collection of microswimmers strongly depends on the hydrodynamic coupling among their constituents and themselves. We present a numerical study for a single and a pair of microswimmers based on lattice Boltzmann method (LBM) simulations. Our numerical algorithm consists of two separable parts. Lagrange polynomials provide a discretization of the microswimmers and the lattice Boltzmann method captures the dynamics of the surrounding fluid. The two components couple via an immersed boundary method. We present data for a single swimmer system and our data also show the onset of collective effects and, in particular, an overall velocity increment of clusters of swimmers.
CRIS-Team Scopus Importer:2023-03-31
Keywords: collective motion; finite element method; Immersed boundary method; lattice Boltzmann method; microswimmer

Lectures on Loop Quantum Gravity - Thiemann, Thomas (Lecture Notes in Physics, 2003)
QGR therefore is, by definition, not a unified theory of all interactions in the standard sense, since such a theory would require a new symmetry principle. However, it unifies all presently known interactions in a new sense by quantum mechanically implementing their common symmetry group, the four-dimensional diffeomorphism group, which is almost completely broken in perturbative approaches.

“Letterier: Categories, Genres, and Epistolarity.” - Sinding, Michael (What is a Letter? Essays on epistolary theory and culture, 2017)
This essay approaches the question ‘What is a letter?’ via two more general questions, ‘What is a genre?’, and ‘What is a category?’ It offers an overview of how concept and category research can help answer these questions; how scholarship on letters might extend category research; and how this cross-fertilization may illuminate epistolary texts, structures, cultures and histories.
Keywords: genre; categories; concepts; letters; epistolarity

Librationen. Durs Grünbein im Dialog zu »Cyrano oder Die Rückkehr vom Mond« und »Vom Schnee oder Descartes in Deutschland« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Lie-Punktsymmetrien erhaltende Quantisierung in der Loop-Quantenkosmologie - Giesel, Kristina; Herzog, Adrian (2014)

Light-induced evaporative cooling of holes in the Hubbard model - Werner, Philipp; Eckstein, Martin; Müller, Markus; Refael, Gil (Nature Communications, 2019)
An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature. Strongly correlated Fermi liquids and symmetry-broken states could thus be produced by dipolar excitations. Using nonequilibrium dynamical mean field theory, we show that suitably designed chirped pulses may realize this cooling effect. In particular, we demonstrate the emergence of antiferromagnetic order in a system which is initially in a weakly correlated state above the maximum Néel temperature. Our work suggests a general strategy for inducing strong correlation phenomena in periodically modulated atomic gases in optical lattices or light-driven materials.
CRIS-Team Scopus Importer:2019-12-17

Light ring behind wormhole throat: Geodesics, images, and shadows - Huang, Hyat; Kunz, Jutta; Yang, Jinbo; Zhang, Cong (Physical Review D, 2023)
The geodesics of the Ellis-Bronnikov wormhole with two parameters are studied. The asymmetric wormhole has only one light ring and one innermost stable circular orbit located on one side of the wormhole throat. Consequently, certain light rays can be reflected back by the wormhole. Additionally, the same wormhole can have different appearances on both sides of the throat. We present novel images of the wormhole with a light ring behind the throat in a scenario with an accretion disk as the light source and in a backlit wormhole scenario, which are distinct from the images of other compact objects and have the potential to be observed.
CRIS-Team Scopus Importer:2023-06-23

Limits of Applicability of the Voronoi Tessellation Determined by Centers of Cell Nuclei to Epithelium Morphology - Kaliman, Sara; Jayachandran, Christina; Rehfeldt, Florian; Smith, Ana-Suncana (Frontiers in Physiology, 2016)
It is well accepted that cells in the tissue can be regarded as tiles tessellating space. A number of approaches were developed to find an appropriate mathematical description of such cell tiling. A particularly useful approach is the so called Voronoi tessellation, built from centers of mass of the cell nuclei (CMVT), which is commonly used for estimating the morphology of cells in epithelial tissues. However, a study providing a statistically sound analysis of this method's accuracy is not available in the literature. We addressed this issue here by comparing a number of morphological measures of the cells, including area, perimeter, and elongation obtained from such a tessellation with identical measures extracted from direct imaging acquired by staining the cell membranes. After analyzing the shapes of 15,000 MDCK II epithelial cells under several conditions, we find that CMVT reasonably well reproduces many of the morphological properties of the tissue with an error that is between 10 and 15%. Moreover, cross-correlations between different morphological measures are reproduced qualitatively correctly by this method. However, all of the properties including the cell perimeters, number of neighbors, and anisotropy measures often suffer from systematic or size dependent errors. These discrepancies originate from the polygonal nature of the tessellation which sets the limits of the applicability of CMVT.
Keywords: epithelial tissue morphology; Voronoi tessellation; fluorescence microscopy; nuclei segmentation; image analysis; MDCK; cross-correlations; cell shape

Linear magnetoresistance in mosaic-like bilayer graphene - Kißlinger, Ferdinand; Ott, Christian; Heide, Christian; Kampert, Erik; Butz, Benjamin; Spiecker, Erdmann; Shallcross, Sam; Weber, Heiko B. (Nature Physics, 2015)
The magnetoresistance of conductors usually has a quadratic dependence on magnetic field(1), however, examples exist of non-saturating linear behaviour in diverse materials(2-6). Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure(7,8). Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations(9,10). We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.

Linear optical elements based on cooperative subwavelength emitter arrays - Baßler, Nico; Reitz, Michael; Schmidt, Kai Phillip; Genes, Claudiu (Optics Express, 2023)
We describe applications of two-dimensional subwavelength quantum emitter arrays as efficient optical elements in the linear regime. For normally incident light, the cooperative optical response, stemming from emitter-emitter dipole exchanges, allows the control of the array's transmission, its resonance frequency, and bandwidth. Operations on fully polarized incident light, such as generic linear and circular polarizers as well as phase retarders can be engineered and described in terms of Jones matrices. Our analytical approach and accompanying numerical simulations identify optimal regimes for such operations and reveal the importance of adjusting the array geometry and of the careful tuning of the external magnetic fields amplitude and direction.
CRIS-Team Scopus Importer:2023-02-24

Linked-cluster expansions for quantum magnets on the hypercubic lattice - Coester, Kris; Joshi, Darshan G.; Vojta, Matthias; Schmidt, Kai Phillip (Physical Review B, 2016)
For arbitrary space dimension d, we investigate the quantum phase transitions of two paradigmatic spin models defined on a hypercubic lattice, the coupled-dimer Heisenberg model and the transverse-field Ising model. To this end, high-order linked-cluster expansions for the ground-state energy and the one-particle gap are performed up to order 9 about the decoupled-dimer and high-field limits, respectively. Extrapolations of the high-order series yield the location of the quantum phase transition and the correlation-length exponent. as a function of space dimension d. The results are complemented by 1/d expansions to next-to-leading order of observables across the phase diagrams. Remarkably, our analysis of the extrapolated linked-cluster expansion allows to extract the coefficients of the full 1/d expansion for the phase-boundary location in both models exactly in leading order and quantitatively for subleading corrections.

Linked cluster expansions via hypergraph decompositions - Mühlhauser, Matthias; Schmidt, Kai Phillip (Physical Review E, 2022)
We propose a hypergraph expansion which facilitates the direct treatment of quantum spin models with many-site interactions via perturbative linked cluster expansions. The main idea is to generate all relevant subclusters and sort them into equivalence classes essentially governed by hypergraph isomorphism. Concretely, a reduced K??nig representation of the hypergraphs is used to make the equivalence relation accessible by graph isomorphism. During this procedure we determine the embedding factor for each equivalence class, which is used in the final resummation in order to obtain the final result. As an instructive example we calculate the ground-state energy and a particular excitation gap of the plaquette Ising model in a transverse field on the three-dimensional cubic lattice.
CRIS-Team WoS Importer:2022-07-01

Linking covariant and canonical loop quantum gravity: New solutions to the Euclidean scalar constraint - Alesci, Emanuele; Thiemann, Thomas; Zipfel, Antonia (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012)
It is often emphasized that spin-foam models could realize a projection on the physical Hilbert space of canonical loop quantum gravity. As a first test, we analyze the one-vertex expansion of a simple Euclidean spin foam. We find that for fixed Barbero-Immirzi parameter gamma = 1, the one-vertex amplitude in the Kaminski, Kisielowski, and Lewandowski prescription annihilates the Euclidean Hamiltonian constraint of loop quantum gravity [T. Thiemann, Classical Quantum Gravity 15, 839 (1998).]. Since, for gamma = 1, the Lorentzian part of the Hamiltonian constraint does not contribute, this gives rise to new solutions of the Euclidean theory. Furthermore, we find that the new states only depend on the diagonal matrix elements of the volume. This seems to be a generic property when applying the spin-foam projector.

Linking covariant and canonical LQG II: spin foam projector - Thiemann, Thomas; Zipfel, Antonia (Classical and Quantum Gravity, 2014)
In a seminal paper, Kaminski et al for the first time extended the definition of spin foam models to arbitrary boundary graphs. This is a prerequisite in order to make contact to the canonical formulation of loop quantum gravity whose Hilbert space contains all these graphs. This makes it finally possible to investigate the question whether any of the presently considered spin foam models yields a rigging map for any of the presently defined Hamiltonian constraint operators. We postulate a rigging map by summing over all abstract spin foams with arbitrary but given boundary graphs. The states induced on the boundary of these spin foams can then be identified with elements in the gauge invariant Hilbert space H-0 of the canonical theory. Of course, such a sum over all spin foams is potentially divergent and requires a regularization. Such a regularization can be obtained by introducing specific cut-offs and a weight for every single foam. Such a weight could be for example derived from a generalized formal group field theory allowing for arbitrary interaction terms. Since such a derivation is, however, technical involved we forgo to present a strict derivation and assume that there exist a weight satisfying certain natural axioms, most importantly a gluing property. These axioms are motivated by the requirement that spin foam amplitudes should define a rigging map ( physical inner product) induced by the Hamiltonian constraint. In the analysis of the resulting object we are able to identify an elementary spin foam transfer matrix that allows to generate any finite foam as a finite power of the transfer matrix. It transpires that the sum over spin foams, as written, does not define a projector on the physical Hilbert space. This statement is independent of the concrete spin foam model and Hamiltonian constraint. However, the transfer matrix potentially contains the necessary ingredient in order to construct a proper rigging map in terms of a modified transfer matrix.
Keywords: loop quantum gravity; spin foam; Hamiltonian constraint; rigging map

Liquid Crystalline Phase Formation in Suspensions of Solid Trimyristin Nanoparticles - Gehrer, Simone; Schmiele, Martin; Westermann, Martin; Steiniger, Frank; Unruh, Tobias (Journal of Physical Chemistry B, 2014)
The presence of liquid crystalline phases in suspensions of solid lipid nanoparticles can increase the risk of their gelling upon administration through fine needles. Here we study the formation of liquid crystalline phases in aqueous suspensions of platelet-like shaped solid lipid nanoparticles. A native lecithin-stabilized trimyristin (20 wt %) suspension was investigated at different dilution levels by small-angle X-ray scattering (SAXS) and visual inspection of their birefringence between two crossed polarizers. For trimyristin concentrations phi(MMM) < 6 wt %, the dispersed platelets are well separated from each other whereas they start to self-assemble into stacked lamellae for 6 wt % <= phi(MMM) < 12 wt %. For phi(MMM) >= 12 wt %, the SAXS patterns become increasingly anisotropic, which is a signature of an evolving formation of a preferred orientation of the platelets on a microscopic scale. Simultaneously, the suspensions become birefringent, which proves the existence of an anisotropic liquid crystalline phase formed in the still low viscous liquid suspensions. Spatially resolved SAXS scans and polarization microscopy indicate rather small domains in the (sub)micrometer size range in the nematic liquid crystalline phase and the presence of birefringent droplets (tactoids). The observed critical concentrations for the formation of stacks and the liquid crystalline phase are significantly higher as for equivalent suspensions prepared from triglycerides with longer chains. This can be explained with the lower aspect ratio of trimyristin platelets. Special emphasis is put on the isotropic-liquid crystalline phase transition as a function of the ionic strength of the dispersion medium and phi(MMM). Higher salt concentrations allow shifting of the phase transition to higher trimyristin concentrations. This can be attributed to a partial screening of the repulsive forces between the platelets, which allows higher packing densities within the platelet stacks and of remaining isolated platelets.

Literarische Mikroskopie des Nanokosmos - Heydenreich, Aura; Mecke, Klaus (Science meets Fiction. Nano-Modellierungen: Poesie und Mikroskopie, 2018)

Literatur- und Naturwissenschaft – Wissenskulturen in Wechselwirkung. Plädoyer für eine interaktionale Diskurszone zwischen den epistemischen Gemeinschaften - Heydenreich, Aura; Mecke, Klaus (Quarks and letters. Naturwissenschaften in der Literatur und Kultur der Gegenwart, 2015)

L lines, C points and Chern numbers: Understanding band structure topology using polarization fields - Fösel, Thomas; Peano, Vittorio; Marquardt, Florian (New Journal of Physics, 2017)
Topology has appeared in different physical contexts. The most prominent application is topologically protected edge transport in condensed matter physics. The Chern number, the topological invariant of gapped Bloch Hamiltonians, is an important quantity in this field. Another example of topology, in polarization physics, are polarization singularities, called L lines and C points. By establishing a connection between these two theories, we develop a novel technique to visualize and potentially measure the Chern number: it can be expressed either as the winding of the polarization azimuth along L lines in reciprocal space, or in terms of the handedness and the index of the C points. For mechanical systems, this is directly connected to the visible motion patterns.
CRIS-Team Scopus Importer:2023-03-27
Keywords: Chern insulators; Chern number; polarization singularities

Local anisotropy of fluids using Minkowski tensors - Kapfer, Sebastian; Mickel, Walter; Schaller, Fabian; Spanner, Markus; Goll, Christian; Nogawa, T.; Ito, Nobuyasu; Mecke, Klaus; Schröder-Turk, Gerd (Journal of Statistical Mechanics-Theory and Experiment, 2010)
Statistics of the free volume available to individual particles have previously been studied for simple and complex fluids, granular matter, amorphous solids, and structural glasses. Minkowski tensors provide a set of shape measures that are based on strong mathematical theorems and easily computed for polygonal and polyhedral bodies such as free volume cells (Voronoi cells). They characterize the local structure beyond the two-point correlation function and are suitable to define indices 0 <= beta(a,b)(v) <= 1 of local anisotropy. Here, we analyze the statistics of Minkowski tensors for configurations of simple liquid models, including the ideal gas (Poisson point process), the hard disks and hard spheres ensemble, and the Lennard-Jones fluid. We show that Minkowski tensors provide a robust characterization of local anisotropy, which ranges from beta(a,b)(v) approximate to 0.3 for vapor phases to beta(a,b)(v) -> 1 for ordered solids. We find that for fluids, local anisotropy decreases monotonically with increasing free volume and randomness of particle positions. Furthermore, the local anisotropy indices beta(a,b)(v) are sensitive to structural transitions in these simple fluids, as has been previously shown in granular systems for the transition from loose to jammed bead packs.
Keywords: granular matter; random/ordered microstructures (theory); monodisperse fluids; mixtures and polydisperse fluids

Local Density Matrices of Many-Body States in the Constant Weight Subspaces - Chen, Jianxin; Han, Muxin; Li, Youning; Zeng, Bei; Zhou, Jie (Reports on Mathematical Physics, 2019)
Let V = ⊗N k=1 Vk be an N-particle Hilbert space, whose individual single-particle space is the one with spin j and dimension d = 2j + 1. Let V(w) be the subspace of V with constant weight w, consisting of vectors whose total spins are w. We show that the combinatorial properties of the constant weight condition impose strong constraints on the reduced density matrices for any vector |ψ) in the constant weight subspace V(w), which limit the possibility of the entanglement structures of |ψ). Our results find applications in the overlapping quantum marginal problem, quantum error-correcting codes, and the spin-network structures in quantum gravity.
CRIS-Team Scopus Importer:2019-06-28
Keywords: constant weight subspace; perfect invariant tensors; reduced density matrix

Local interpretation of time-resolved x-ray absorption in Mott insulators: Insights from nonequilibrium dynamical mean-field theory - Werner, Philipp; Golez, Denis; Eckstein, Martin (Physical Review B, 2022)
We present a formalism based on nonequilibrium dynamical mean-field theory (DMFT) which allows to compute the time-resolved x-ray absorption spectrum (XAS) of photoexcited solids. By applying this formalism to the photodoped half-filled and quarter-filled two-orbital Hubbard models in the Mott insulating regime we clarify how the time-resolved XAS signal reflects the nonequilibrium population of different local states. Apart from the missing broadening associated with continuum excitations, the atomic XAS spectrum computed with the nonthermal state populations provides a good approximation to the full nonequilibrium DMFT result. This suggests a route to combine the accurate DMFT description of nonequilibrium states of solids with cluster calculations of the XAS signal.
CRIS-Team WoS Importer:2022-11-11

Local orientations of fluctuating fluid interfaces - Mecke, Klaus; et al. (Journal of Chemical Physics, 2005)
Thermal fluctuations cause the local normal vectors of fluid interfaces to deviate from the vertical direction defined by the flat mean interface position. This leads to a nonzero mean value of the corresponding polar tilt angle which renders a characterization of the thermal state of an interface. Based on the concept of an effective interface Hamiltonian we determine the variances of the local interface position and of its lateral derivatives. This leads to the probability distribution functions for the metric of the interface and for the tilt angle which allows us to calculate its mean value and its mean-square deviation. We compare the temperature dependences of these quantities as predicted by the simple capillary-wave model, by an improved phenomenological model, and by the microscopic effective interface Hamiltonian derived from density-functional theory. The mean tilt angle discriminates clearly between these theoretical approaches and emphasizes the importance of the variation of the surface tension at small wavelengths. Also the tilt angle two-point correlation function is determined which renders an additional structural characterization of interfacial fluctuations. Various experimental accesses to measure the local orientational fluctuations are discussed.

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In particulate soft matter systems the average number of contacts extitZ of a particle is an important predictor of the mechanical properties of the system. Using x-ray tomography, we analyze packings of frictional, oblate ellipsoids of various aspect ratios α, prepared at different global volume fractions ϕ extitg

Long-Range Coulomb Interactions in Surface Systems: A First-Principles Description within Self-Consistently Combined GW and Dynamical Mean-Field Theory - Hansmann, Philipp; Ayral, Thomas; Vaugier, L.; Werner, Philipp; Biermann, Silke (Physical Review Letters, 2013)
Systems of adatoms on semiconductor surfaces display competing ground states and exotic spectral properties typical of two-dimensional correlated electron materials which are dominated by a complex interplay of spin and charge degrees of freedom. We report a fully ab initio derivation of low-energy Hamiltonians for the adatom systems Si(111) : X, with X = Sn, Si, C, Pb, that we solve within self-consistently combined GW and dynamical mean-field theory. Calculated photoemission spectra are in agreement with available experimental data. We rationalize experimentally observed trends from Mott physics toward charge ordering along the series as resulting from substantial long-range interactions. DOI: 10.1103/PhysRevLett.110.166401
CRIS-Team WoS Importer:2020-02-19

Loop Quantization of Supergravity Theories - Bodendorfer, Norbert; Thiemann, Thomas (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2013)

Loop quantum gravity - Thiemann, Thomas (Approaches to quantum gravity: Toward a new understanding of space, time and matter, 2008)
We describe the canonical approach to quantum gravity and report on the status of its most advanced implementation, Loop Quantum Gravity (LQG).

Loop quantum gravity coupled to a scalar field - Lewandowski, Jerzy; Sahlmann, Hanno (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2016)
We consider the model of gravity coupled to the Klein-Gordon time field. We do not deparametrize the theory using the scalar field before quantization, but quantize all degrees of freedom. Several new results for loop quantum gravity are obtained: (i) a Hilbert space for the gravity-matter system and a nonstandard representation of the scalar field thereon is constructed, (ii) a new operator for the scalar constraint of the coupled system is defined and investigated, (iii) methods for solving the constraint are developed. Commutators of the new quantum constraint operators correspond to the quantization of the Poisson bracket. This, however, poses problems for finding solutions. Hence the states we consider - and perhaps the whole setup - still needs some improvement. As a side result we describe a representation of the gravitational degrees of freedom in which the flux is diagonal. This representation is related to the BF theory vacuum of Dittrich and Geiller.

Loop quantum gravity on dynamical lattice and improved cosmological effective dynamics with inflaton - Han, Muxin; Liu, Hongguang (Physical Review D, 2021)
In the path integral formulation of the reduced phase space loop quantum gravity (LQG), we propose a new approach to allow the spatial cubic lattice (graph) to change dynamically in the physical time evolution. The equations of motion of the path integral derive the effective dynamics of cosmology from the full LQG, when we focus on solutions with homogeneous and isotropic symmetry. The resulting cosmological effective dynamics with the dynamical lattice improves the effective dynamics obtained earlier from the path integral with a fixed spatial lattice: The improved effective dynamics recovers the Friedmann-Lemaître-Robertson-Walker cosmology at low energy density and resolves the big-bang singularity with a bounce. The critical density ρc at the bounce is Planckian ρc∼Δ-1, where Δ is a Planckian area serving as a certain UV cutoff of the effective theory. The effective dynamics gives the unsymmetric bounce and has the de Sitter (dS) spacetime in the past of the bounce. The cosmological constant Λeff of the dS spacetime is eme
CRIS-Team Scopus Importer:2021-07-16

Loop quantum gravity phenomenology and the issue of Lorentz invariance - Sahlmann, Hanno; Bojowald, Martin; Morales-Tecotl, Hugo (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2005)
A simple model is constructed which allows to compute modified dispersion relations with effects from loop quantum gravity. Different quantization choices can be realized and their effects on the order of corrections studied explicitly. A comparison with more involved semiclassical techniques shows that there is agreement even at a quantitative level. Furthermore, by contrasting Hamiltonian and Lagrangian descriptions we show that possible Lorentz symmetry violations may be blurred as an artifact of the approximation scheme. Whether this is the case in a purely Hamiltonian analysis can be resolved by an improvement in the effective semiclassical analysis. © 2005 The American Physical Society.

Loop Quantum Gravity. The first 30 years. - Giesel, Kristina; Laddha, Alok; Varadarajan, Madhavan; Bianchi, Eugenio; Oriti, Daniele; Dittrich, Biancha; Agullo, Ivan; Singh, Parampreet; Fernando, Barbero; Perez, Alejandro; Barrau, Aurilien; Grain, Julien (World Scientific, 2017)
This volume presents a snapshot of the state-of-the-art in loop quantum gravity from the perspective of younger leading researchers. It takes the reader from the basics to recent advances, thereby bridging an important gap. The aim is two-fold — to provide a contemporary introduction to the entire field for students and post-docs, and to present an overview of the current status for more senior researchers. The contributions include the latest developments that are not discussed in existing books, particularly recent advances in quantum dynamics both in the Hamiltonian and sum over histories approaches; and applications to cosmology of the early universe and to the quantum aspects of black holes.

Loop quantum gravity vacuum with nondegenerate geometry - Sahlmann, Hanno; et al. (Symmetry Integrability and Geometry-Methods and Applications, 2012)
In loop quantum gravity, states of the gravitational field turn out to be excitations over a vacuum state that is sharply peaked on a degenerate spatial geometry. While this vacuum is singled out as fundamental due to its invariance properties, it is also important to consider states that describe non-degenerate geometries. Such states have features of Bose condensate ground states. We discuss their construction for the Lie algebra as well as the Weyl algebra setting, and point out possible applications in effective field theory, Loop Quantum Cosmology, as well as further generalizations.
Keywords: Geometric condensate; Loop quantum gravity; Representations

Low-energy effective theory of the toric code model in a parallel magnetic field - Vidal, Julien; Dusuel, Sebastien; Schmidt, Kai Phillip (Physical Review B, 2009)
We determine analytically the phase diagram of the toric code model in a parallel magnetic field which displays three distinct regions. Our study relies on two high-order perturbative expansions in the strong- and weak-field limits, as well as a large-spin analysis. Calculations in the topological phase establish a quasiparticle picture for the anyonic excitations. We obtain two second-order transition lines that merge with a first-order line, giving rise to a multicritical point as recently suggested by numerical simulations. We compute the values of the corresponding critical fields and exponents that drive the closure of the gap. We also give the one-particle dispersions of the anyonic quasiparticles inside the topological phase.
Keywords: magnetic fields; quantum theory

Low-Lying Electronic Excited States of Pentacene Oligomers: A Comparative Electronic Structure Study in the Context of Singlet Fission - Brana Coto, Pedro; Sharifzadeh, Sahar; Neaton, Jeffrey B.; Thoss, Michael (Journal of Chemical Theory and Computation, 2015)
The lowest-lying electronic excited states of pentacene and its oligomers are investigated using accurate multireference wave function methods (CASPT2/CASSCF) and the many-body Greens’s function approach (GW/BSE). The results obtained for dimers and trimers of different geometry reveal a complex electronic structure, which includes locally excited, charge transfer, and multiexciton states. For singlets of single-excitation character, both approaches yield excitation energies that are in good overall quantitative agreement. While the multiexciton states are located relatively high in energy in all systems investigated, charge transfer states exist in close proximity to the lowest-lying absorbing states. The implications of the results for the mechanisms of singlet fission in pentacene are discussed.

LTB spacetimes in terms of Dirac observables - Giesel, Kristina; Tambornino, Johannes; Thiemann, Thomas (Classical and Quantum Gravity, 2010)
The construction of Dirac observables, that is, gauge-invariant objects, in general relativity is technically more complicated than in other gauge theories such as the standard model due to its more complicated gauge group which is closely related to the group of spacetime diffeomorphisms. However, the explicit and usually cumbersome expression of Dirac observables in terms of gauge noninvariant quantities is irrelevant if their Poisson algebra is sufficiently simple. Precisely that can be achieved by employing the relational formalism and a specific type of matter proposed originally by Brown and Kuchar, namely pressureless dust fields. Moreover one is able to derive a compact expression for a physical Hamiltonian that drives their physical time evolution. The resulting gauge-invariant Hamiltonian system is obtained by Higgs-ing the dust scalar fields and has an infinite number of conserved charges which force the Goldstone bosons to decouple from the evolution. In previous publications we have shown that explicitly for cosmological perturbations. In this paper we analyse the spherically symmetric sector of the theory and it turns out that the solutions are in one-to-one correspondence with the class of Lemaitre-Tolman-Bondi metrics. Therefore, the theory is capable of properly describing the whole class of gravitational experiments that rely on the assumption of spherical symmetry.

Machine learning and quantum devices - Marquardt, Florian (2021)
These brief lecture notes cover the basics of neural networks and deep learning as well as their applications in the quantum domain, for physicists without prior knowledge. In the first part, we describe training using backpropagation, image classification, convolutional networks and autoencoders. The second part is about advanced techniques like reinforcement learning (for discovering control strategies), recurrent neural networks (for analyzing time traces), and Boltzmann machines (for learning probability distributions). In the third lecture, we discuss first recent applications to quantum physics, with an emphasis on quantum information processing machines. Finally, the fourth lecture is devoted to the promise of using quantum effects to accelerate machine learning.
CRIS-Team Scopus Importer:2023-03-27

Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition - Loskill, Peter; Puthoff, Jonathan; Wilkinson, Matt; Mecke, Klaus; Jacobs, Karin; Autumn, Kellar (Journal of the Royal Society Interface, 2013)
Surface energies are commonly used to determine the adhesion forces between materials. However, the component of surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers. Previous theoretical results and indirect experimental evidence suggest that the van der Waals energies of subsurface layers will influence interfacial adhesion forces. We discovered that nanometre-scale differences in the oxide layer thickness of silicon wafers result in significant macroscale differences in the adhesion of isolated gecko setal arrays. Si/SiO2 bilayer materials exhibited stronger adhesion when the SiO2 layer is thin (approx. 2 nm). To further explore how layered materials influence adhesion, we functionalized similar substrates with an octadecyltrichlorosilane monolayer and again identified a significant influence of the SiO2 layer thickness on adhesion. Our theoretical calculations describe how variation in the SiO2 layer thickness produces differences in the van der Waals interaction potential, and these differences are reflected in the adhesion mechanics. Setal arrays used as tribological probes provide the first empirical evidence that the 'subsurface energy' of inhomogeneous materials influences the macroscopic surface forces.
Keywords: van der Waals forces; gecko adhesion; surface energy

Magnetic Chern bands and triplon Hall effect in an extended Shastry-Sutherland model - Malki, Maik; Schmidt, Kai Phillip (Physical Review B, 2017)
We study topological properties of one-triplon bands in an extended Shastry-Sutherland model relevant for the frustrated quantum magnet SrCu2(BO3)(2). To this end perturbative continuous unitary transformations are applied about the isolated dimer limit allowing us to calculate the one-triplon dispersion up to high order in various couplings including intra-and interdimer Dzyaloshinskii-Moriya interactions and a general uniform magnetic field. We determine the Berry curvature and the Chern number of the different one-triplon bands. We demonstrate the occurrence of Chern numbers +/- 1 and +/- 2 for the case that two components of the magnetic field are finite. Finally, we also calculate the triplon Hall effect arising at finite temperatures.

Magnetic correlations in infinite-layer nickelates: An experimental and theoretical multimethod study - Ortiz, R. A.; Puphal, P.; Klett, M.; Hotz, F.; Kremer, R. K.; Trepka, H.; Hemmida, M.; Von Nidda, H-A Krug; Isobe, M.; Khasanov, R.; Luetkens, H.; Hansmann, Philipp; et al. (Physical Review Research, 2022)
We report a comprehensive study of magnetic correlations in LaNiO2, a parent compound of the recently discovered family of infinite-layer (IL) nickelate superconductors, using multiple experimental and theoretical methods. Our specific heat, muon-spin rotation (µSR), and magnetic susceptibility measurements on polycrystalline LaNiO2 show that long-range magnetic order remains absent down to 2 K. Nevertheless, we detect residual entropy in the low-temperature specific heat, which is compatible with a model fit that includes paramagnon excitations. The µSR and low-field static and dynamic magnetic susceptibility measurements indicate the presence of short-range magnetic correlations and glassy spin dynamics, which we attribute to local oxygen nonstoichiometry in the average infinite-layer crystal structure. This glassy behavior can be suppressed in strong external fields, allowing us to extract the intrinsic paramagnetic susceptibility. Remarkably, we find that the intrinsic susceptibility shows non-Curie-Weiss behavior at high temperatures, in analogy to doped cuprates that possess robust nonlocal spin fluctuations. The distinct temperature dependence of the intrinsic susceptibility of LaNiO2 can be theoretically understood by a multimethod study of the single-band Hubbard model in which we apply complementary cutting-edge quantum many-body techniques (dynamical mean-field theory, cellular dynamical mean-field theory, and the dynamical vertex approximation) to investigate the influence of both short- and long-ranged correlations. Our results suggest a profound analogy between the magnetic correlations in parent (undoped) IL nickelates and doped cuprates.
CRIS-Team Scopus Importer:2022-06-10

Magnetic Excitations in Bilayer High-Temperature Superconductors with Stripe Correlations - Schmidt, Kai Phillip; et al. (Journal of the Physical Society of Japan, 2005)
The universal behaviour of the magnetic excitations in high-temperature superconductors is described in a model with static stripes retaining only the localized spin degrees of freedom. The stripes are represented by a model of coupled two-leg spin ladders. We start from the results obtained previously by continuous unitary transformations for an isolated spin ladder. A quantitative description of neutron scattering data is reached, using a model for a single cuprate layer with well established values of the exchange coupling constants. The neutron resonance peak is explained in terms of a saddle point in the dispersion of the magnetic excitations. Here we make predictions for bilayer systems with in-phase or out-of-phase stripe correlations. The results may serve as a guide for future experimental analyses.
Keywords: magnetic excitations; spectral densities; stripe phase; inelastic neutron scattering; high-temperature superconductors

Magnetic excitations in the stripe phase of high-T-c superconductors - Schmidt, Kai Phillip; et al. (ELSEVIER SCIENCE BV, 2005)
The magnetic excitations in the stripe phase of high-T-c superconductors are investigated in a model of spin ladders which are effectively coupled via charged stripes. Starting from the effective single-triplon model for the isolated spin ladder, the quasi-one-dimensional spin system can be described straightforwardly. Very good agreement is obtained with recent neutron scattering data on La15/8Ba1/8CuO4 (no spin gap) and YBa2Cu3O6.6 (gapped). The signature of quasi-one-dimensional spin physics in a single-domain stripe phase is predicted. (c) 2004 Elsevier B.V. All rights reserved.
Keywords: superconductors; high T-c; neutron scattering; inelastic; antiferromagnetism; quantum; spin dynamics

Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory - Schmidt, Kai Phillip; et al. (PERGAMON-ELSEVIER SCIENCE LTD, 2002)
Magnetic excitations in two-leg S = 1/2 ladders are studied both experimentally and theoretically. Experimentally, we report on the reflectivity, the transmittance and the optical conductivity sigma(omega) of undoped LaxCa14-xCu24O41 for x = 4, 5, and 5.2. Using two different theoretical approaches (Jordan-Wigner fermions and perturbation theory), we calculate the dispersion of the elementary triplets, the optical conductivity and the momentum-resolved spectral density of two-triplet excitations for 0.2 less than or equal to J( )/J(perpendicular to) less than or equal to 1.2. We discuss phonon-assisted two-triplet absorption, the existence of two-triplet bound states, the two-triplet continuum, and the size of the exchange parameters. (C) 2002 Elsevier Science Ltd. All rights reserved.
Keywords: infrared spectroscopy; magnetic properties

Magnetic ordering induced by interladder coupling in the spin-1/2 Heisenberg two-leg ladder antiferromagnet C9H18N2CuBr4 - Hong, Tao; Schmidt, Kai Phillip; Coester, K.; Awwadi, F. F.; Turnbull, M. M.; Qiu, Y.; Rodriguez-Rivera, J. A.; Zhu, M.; Ke, X.; Aoyama, C. P.; Takano, Y.; Cao, Huibo; et al. (Physical Review B, 2014)
We present specific-heat and neutron-scattering results for the S = 1/2 quantum antiferromagnet (dimethylammonium)(3,5-dimethylpyridinium)CuBr4. The material orders magnetically at T-N = 1.99(2) K, and magnetic excitations are accompanied by an energy gap of 0.30(2) meV due to spin anisotropy. The system is best described as coupled two-leg spin-1/2 ladders with the leg exchange J(leg) = 0.60(2) meV, rung exchange J(rung) = 0.64(9) meV, interladder exchange J(int) = 0.19(2) meV, and an interaction-anisotropy parameter lambda = 0.93(2), according to inelastic neutron-scattering measurements. In contrast to most spin ladders reported to date, the material is a rare example in which the interladder coupling is very near the critical value required to drive the system to a Neel-ordered phase without the assistance of a magnetic field.

Magnetic Properties and Pseudogap Formation in Infinite-Layer Nickelates: Insights From the Single-Band Hubbard Model - Klett, Marcel; Hansmann, Philipp; Schäfer, Thomas (Frontiers in Physics, 2022)
We study the magnetic and spectral properties of a single-band Hubbard model for the infinite-layer nickelate compound LaNiO2. As spatial correlations turn out to be the key ingredient for understanding its physics, we use two complementary extensions of the dynamical mean-field theory to take them into account: the cellular dynamical mean-field theory and the dynamical vertex approximation. Additionally to the systematic analysis of the doping dependence of the non-Curie-Weiss behavior of the uniform magnetic susceptibility, we provide insight into its relation to the formation of a pseudogap regime by the calculation of the one-particle spectral function and the magnetic correlation length. The latter is of the order of a few lattice spacings when the pseudogap opens, indicating a strong-coupling pseudogap formation in analogy to cuprates.
CRIS-Team Scopus Importer:2022-03-18
Keywords: cellular dynamical mean field theory; dynamical mean-field theory (DMFT); dynamical vertex approximation; hubbard model; magnetism; nickelates; pseudogap

Magnetization of SrCu2(BO3)(2) in Ultrahigh Magnetic Fields up to 118 T - Matsuda, Y. H.; Abe, N.; Takeyama, S.; Kageyama, Hiroshi; Corboz, P.; Honecker, Andreas; Manmana, S. R.; Foltin, G. R.; Schmidt, Kai Phillip; Mila, F. (Physical Review Letters, 2013)
The magnetization process of the orthogonal-dimer antiferromagnet SrCu2(BO3)(2) is investigated in high magnetic fields of up to 118 T. A 1/2 plateau is clearly observed in the field range 84 to 108 T in addition to 1/8, 1/4, and 1/3 plateaus at lower fields. Using a combination of state-of-the-art numerical simulations, the main features of the high-field magnetization, a 1/2 plateau of width 24 T, a 1/3 plateau of width 34 T, and no 2/5 plateau, are shown to agree quantitatively with the Shastry-Sutherland model if the ratio of inter-to intradimer exchange interactions J'/J = 0.63. It is further predicted that the intermediate phase between the 1/3 and 1/2 plateaus is not uniform but consists of a 1/3 supersolid followed by a 2/5 supersolid and possibly a domain-wall phase, with a reentrance into the 1/3 supersolid above the 1/2 plateau.

Magnetization plateaux in an extended Shastry-Sutherland model - Schmidt, Kai Phillip; Dorier, Julien; Mila, Frederic (2009)
We study an extended two-dimensional Shastry-Sutherland model in a magnetic field where besides the usual Heisenberg exchanges of the Shastry-Sutherland model two additional SU(2) invariant couplings are included. Perturbative continous unitary transformations are used to determine the leading order effects of the additional couplings on the pure hopping and on the long-range interactions between the triplons which are the most relevant terms for small magnetization. We then compare the energy of various magnetization plateaux in the classical limit and we discuss the implications for the two-dimensional quantum magnet SrCu(2)(BO(3))(2).

Magnon heralding in cavity optomagnonics - Bittencourt, Victor A. S. V.; Feulner, Verena; Viola Kusminskiy, Silvia (Physical Review A, 2019)
In the emerging field of cavity optomagnonics, photons are coupled coherently to magnons in solid-state systems. These new systems are promising for implementing hybrid quantum technologies. Being able to prepare Fock states in such platforms is an essential step towards the implementation of quantum information schemes. We propose a magnon-heralding protocol to generate a magnon Fock state by detecting an optical cavity photon. Due to the peculiarities of the optomagnonic coupling, the protocol involves two distinct cavity photon modes. Solving the quantum Langevin equations of the coupled system, we show that the temporal scale of the heralding is governed by the magnon-photon cooperativity and derive the requirements for generating high fidelity magnon Fock states. We show that the nonclassical character of the heralded state, which is imprinted in the autocorrelation of an optical "read" mode, is only limited by the magnon lifetime for small enough temperatures. We address the detrimental effects of nonvacuum initial states, showing that high fidelity Fock states can be achieved by actively cooling the system prior to the protocol.
CRIS-Team WoS Importer:2019-07-23

Magnon-Phonon Quantum Correlation Thermometry - Potts, C. A.; Bittencourt, V. A. S. V.; Viola Kusminskiy, Silvia; Davis, J. P. (Physical Review Applied, 2020)
A large fraction of quantum science and technology requires low-temperature environments such as those afforded by dilution refrigerators. In these cryogenic environments, accurate thermometry can be difficult to implement, expensive, and often requires calibration to an external reference. Here, we theoretically propose a primary thermometer based on measurement of a hybrid system consisting of phonons coupled via a magnetostrictive interaction to magnons. Thermometry is based on a cross-correlation measurement in which the spectrum of back-action driven motion is used to scale the thermomechanical motion, providing a direct measurement of the phonon temperature independent of experimental parameters. Combined with a simple low-temperature compatible microwave cavity readout, this primary thermometer is expected to become a promising alternative for thermometry below 1 K.
CRIS-Team WoS Importer:2020-06-16

Manifestly Gauge Invariant Cosmological Perturbation Theory - Zilker, Thomas; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2013)

Manifestly gauge-invariant cosmological perturbation theory from full loop quantum gravity - Han, Muxin; Li, Haida; Liu, Hongguang (Physical Review D, 2020)
We apply the full theory of Loop Quantum Gravity (LQG) to cosmology and present a top-down derivation of gauge-invariant cosmological perturbation theory from quantum gravity. The derivation employs the reduced phase space formulation of LQG and the new discrete path integral formulation defined in M. Han and H. Liu, Phys. Rev. D 101, 046003 (2020). We demonstrate that in the semiclassical approximation and continuum limit, the result coincides with the existing formulation of gauge-invariant cosmological perturbation theory in, e.g., K. Giesel et al., Classical Quantum Gravity 27, 055006 (2010). Time evolution of cosmological perturbations is computed numerically from the new cosmological perturbation theory of LQG, and various power spectrums are studied for scalar mode and tensor mode perturbations. Comparing these power spectrums with predictions from the classical theory demonstrate corrections in the ultralong wavelength regime. These corrections are results from the lattice discretization in LQG. In addition, tensor mode perturbations at late time demonstrate the emergence of spin-2 gravitons as low energy excitations from LQG. The graviton has a modified dispersion relation and reduces to the standard graviton in the long wavelength limit.
CRIS-Team WoS Importer:2021-01-01

Manifestly gauge-invariant general relativistic perturbation theory: I. Foundations - Giesel, Kristina; Hofmann, Stefan; Thiemann, Thomas; Winkler, Oliver (Classical and Quantum Gravity, 2010)
Linear cosmological perturbation theory is pivotal to a theoretical understanding of current cosmological experimental data provided e. g. by cosmic microwave anisotropy probes. A key issue in that theory is to extract the gauge-invariant degrees of freedom which allow unambiguous comparison between theory and experiment. When one goes beyond first (linear) order, the task of writing the Einstein equations expanded to nth order in terms of quantities that are gauge-invariant up to terms of higher orders becomes highly non-trivial and cumbersome. This fact has prevented progress for instance on the issue of the stability of linear perturbation theory and is a subject of current debate in the literature. In this series of papers we circumvent these difficulties by passing to a manifestly gauge-invariant framework. In other words, we only perturb gauge-invariant, i.e. measurable quantities, rather than gauge variant ones. Thus, gauge invariance is preserved non-perturbatively while we construct the perturbation theory for the equations of motion for the gauge-invariant observables to all orders. In this first paper we develop the general framework which is based on a seminal paper due to Brown and Kuchar as well as the relational formalism due to Rovelli. In the second, companion, paper we apply our general theory to FRW cosmologies and derive the deviations from the standard treatment in linear order. As it turns out, these deviations are negligible in the late universe, thus our theory is in agreement with the standard treatment. However, the real strength of our formalism is that it admits a straightforward and unambiguous, gauge-invariant generalization to higher orders. This will also allow us to settle the stability issue in a future publication.

Manifestly gauge-invariant general relativistic perturbation theory: II. FRW background and first order - Giesel, Kristina; Hofmann, Stefan; Thiemann, Thomas; Winkler, Oliver (Classical and Quantum Gravity, 2010)
In our companion paper we identified a complete set of manifestly gauge-invariant observables for general relativity. This was possible by coupling the system of gravity and matter to pressureless dust which plays the role of a dynamically coupled observer. the evolution of those observables is governed by a physical Hamiltonian and we derived the corresponding equations of motion. Linear perturbation theory of those equations of motion around a general exact solution in terms of manifestly gauge-invariant perturbations was then developed. In this paper we specialize our previous results to an FRW background which is also a solution of our modified equations of motion. We then compare the resulting equations with those derived in standard cosmological perturbation theory (SCPT). We exhibit the precise relation between our manifestly gauge-invariant perturbations and the linearly gauge-invariant variables in SCPT. We find that our equations of motion can be cast into SCPT form plus corrections. These corrections are the trace that the dust leaves on the system in terms of a conserved energy-momentum current density. In turns out that these corrections decay; in fact, in the late universe they are negligible whatever the value of the conserved current. We conclude that the addition of dust which serves as a test observer medium, while implying modifications of Einstein's equations without dust, leads to acceptable agreement with known results, while having the advantage that one now talks about manifestly gauge-invariant, that is measurable, quantities, which can be used even in perturbation theory at higher orders.

Manifestly gauge invariant perturbations of scalar-tensor theories of gravity - Han, Yu; Giesel, Kristina; Ma, Yongge (Classical and Quantum Gravity, 2015)
The general relativistic perturbations of scalar-tensor theories (STT) of gravity are studied in a manifestly gauge invariant Hamiltonian formalism. After the derivation of the Hamiltonian equations of motion in this framework, the gauge invariant formalism is used to compute the evolution equations of linear perturbations around a general relativistic spacetime background in the Jordan frame. These equations are then specialized to the case of a flat FRW cosmological background. Furthermore, the equivalence between the Jordan frame and the Einstein frame of STT in the manifestly gauge invariant Hamiltonian formalism is analyzed, and it is shown that also in this framework they can be related by a conformal transformation. Finally, the obtained evolution equations for the linear perturbations in our formalism are compared with those in the standard cosmological perturbation theory. It turns out that the perturbation equations in the two different formalisms coincide with each other in a suitable limit.
Keywords: scalar-tensor theories of gravity; cosmological perturbation theory; manifestly gauge invariant perturbations

Manipulating Intertwined Orders in Solids with Quantum Light - Li, Jiajun; Eckstein, Martin (Physical Review Letters, 2020)
Intertwined orders exist ubiquitously in strongly correlated electronic systems and lead to intriguing phenomena in quantum materials. In this Letter, we explore the unique opportunity of manipulating intertwined orders through entangling electronic states with quantum light. Using a quantum Floquet formalism to study the cavity-mediated interaction, we show the vacuum fluctuations effectively enhance the charge-density-wave correlation, giving rise to a phase with entangled electronic order and photon coherence, with putative superradiant behaviors in the thermodynamic limit. Furthermore, upon injecting even one single photon in the cavity, different orders, including s-wave and eta-paired superconductivity, can be selectively enhanced. Our study suggests a new and generalizable pathway to control intertwined orders and create light-matter entanglement in quantum materials. The mechanism and methodology can be readily generalized to more complicated scenarios.
CRIS-Team WoS Importer:2020-12-11

Many-Body Dephasing in a Trapped-Ion Quantum Simulator - Kaplan, Harvey B.; Guo, Lingzhen; Tan, Wen Lin; De, Arinjoy; Marquardt, Florian; Pagano, Guido; Monroe, Christopher (Physical Review Letters, 2020)
How a closed interacting quantum many-body system relaxes and dephases as a function of time is a fundamental question in thermodynamic and statistical physics. In this Letter, we analyze and observe the persistent temporal fluctuations after a quantum quench of a tunable long-range interacting transverse-field Ising Hamiltonian realized with a trapped-ion quantum simulator. We measure the temporal fluctuations in the average magnetization of a finite-size system of spin-1/2 particles. We experiment in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions for the long-time nonintegrable dynamics. The analytical expression for the temporal fluctuations predicts the exponential suppression of temporal fluctuations with increasing system size. Our measurement data is consistent with our theory predicting the regime of many-body dephasing.
CRIS-Team WoS Importer:2020-10-09

Many-Particle Dephasing after a Quench - Kiendl, Thomas; Marquardt, Florian (Physical Review Letters, 2017)
After a quench in a quantum many-body system, expectation values tend to relax towards long-time averages. However, temporal fluctuations remain in the long-time limit, and it is crucial to study the suppression of these fluctuations with increasing system size. The particularly important case of nonintegrable models has been addressed so far only by numerics and conjectures based on analytical bounds. In this work, we are able to derive analytical predictions for the temporal fluctuations in a nonintegrable model (the transverse Ising chain with extra terms). Our results are based on identifying a dynamical regime of "many-particle dephasing," where quasiparticles do not yet relax but fluctuations are nonetheless suppressed exponentially by weak integrability breaking.
CRIS-Team Scopus Importer:2023-03-27

Mapping the glassy dynamics of soft spheres onto hard-sphere behavior - Schmiedeberg, Michael; Haxton, Tom; Nagel, Sidney; Liu, Andrea (EPL - Europhysics Letters, 2011)
We show that the dynamics of soft-sphere systems with purely repulsive interactions can be described by introducing an effective hard-sphere diameter determined using the Andersen-Weeks-Chandler approximation. We find that this approximation, known to describe static properties of liquids, also gives a good description of a dynamical quantity, the relaxation time, even in the vicinity of the glass transition. Copyright (C) EPLA, 2011

Matrix elements of Lorentzian Hamiltonian constraint in loop quantum gravity - Liegener, Klaus; Alesci, Emanuele; Zipfel, Antonia (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2013)
The Hamiltonian constraint is the key element of the canonical formulation of loop quantum gravity (LQG) coding its dynamics. In Ashtekar-Barbero variables it naturally splits into the so-called Euclidean and Lorentzian parts. However, due to the high complexity of this operator, only the matrix elements of the Euclidean part have been considered so far. Here we evaluate the action of the full constraint, including the Lorentzian part. The computation requires heavy use of SU(2) recoupling theory and several tricky identities among n-j symbols are used to find the final result: these identities, together with the graphical calculus used to derive them, also simplify the Euclidean constraint and are of general interest in LQG computations. © 2013 American Physical Society.

Maturation of monocyte-derived DCs leads to increased cellular stiffness, higher membrane fluidity, and changed lipid composition - Lühr, Jennifer; Alex, Nils; Amon, Lukas; Kraeter, Martin; Kubankova, Marketa; Sezgin, Erdinc; Lehmann, Christian; Heger, Lukas; Heidkamp, Gordon Frederik; Smith, Ana-Suncana; Zaburdaev, Vasily; Böckmann, Rainer; et al. (EUROPEAN JOURNAL OF IMMUNOLOGY, 2021)
CRIS-Team WoS Importer:2022-03-11

Maturation of Monocyte-Derived DCs Leads to Increased Cellular Stiffness, Higher Membrane Fluidity, and Changed Lipid Composition - Luhr, Jennifer J.; Alex, Nils; Amon, Lukas; Krater, Martin; Kubankova, Marketa; Sezgin, Erdinc; Lehmann, Christian; Heger, Lukas; Heidkamp, Gordon Frederik; Smith, Ana-Suncana; Zaburdaev, Vasily; Böckmann, Rainer; et al. (Frontiers in Immunology, 2020)
Dendritic cells (DCs) are professional antigen-presenting cells of the immune system. Upon sensing pathogenic material in their environment, DCs start to mature, which includes cellular processes, such as antigen uptake, processing and presentation, as well as upregulation of costimulatory molecules and cytokine secretion. During maturation, DCs detach from peripheral tissues, migrate to the nearest lymph node, and find their way into the correct position in the net of the lymph node microenvironment to meet and interact with the respective T cells. We hypothesize that the maturation of DCs is well prepared and optimized leading to processes that alter various cellular characteristics from mechanics and metabolism to membrane properties. Here, we investigated the mechanical properties of monocyte-derived dendritic cells (moDCs) using real-time deformability cytometry to measure cytoskeletal changes and found that mature moDCs were stiffer compared to immature moDCs. These cellular changes likely play an important role in the processes of cell migration and T cell activation. As lipids constitute the building blocks of the plasma membrane, which, during maturation, need to adapt to the environment for migration and DC-T cell interaction, we performed an unbiased high-throughput lipidomics screening to identify the lipidome of moDCs. These analyses revealed that the overall lipid composition was significantly changed during moDC maturation, even implying an increase of storage lipids and differences of the relative abundance of membrane lipids upon maturation. Further, metadata analyses demonstrated that lipid changes were associated with the serum low-density lipoprotein (LDL) and cholesterol levels in the blood of the donors. Finally, using lipid packing imaging we found that the membrane of mature moDCs revealed a higher fluidity compared to immature moDCs. This comprehensive and quantitative characterization of maturation associated changes in moDCs sets the stage for improving their use in clinical application.
CRIS-Team Scopus Importer:2020-12-25
Keywords: cell mechanics; cellular stiffness; cholesterol; lipidomics; lipids; low-density lipoprotein; maturation; monocyte-derived dendritic cells

Mean field approach of dynamical pattern formation in underdamped active matter with short-ranged alignment and distant anti-alignment interactions - Arold, Dominic; Schmiedeberg, Michael (Journal of Physics: Condensed Matter, 2020)
Many active matter systems, especially on the microscopic scale, are well approximated as overdamped, meaning that any inertial momentum is immediately dissipated by the environment. On the other hand, especially for macroscopic active systems but also for many mesoscopic systems the time scale of translational inertial motion can become large enough to be relevant for the dynamics. This raises the question how collective dynamics and the resulting states in active matter are influenced by inertia. Therefore, we propose a coarse-grained continuum model for underdamped active matter based on a mean field description for passive systems. Furthermore, as an example, we apply the model to a system with interactions that support an alignment on short distances and an anti-alignment on longer length scales as known in the context of pattern formation due to orientational interactions. Our numerical calculations of the under- and overdamped dynamics both predict a structured laning state. However, activity induced convective flows that are only present in the underdamped model destabilize this state when the anti-alignment is weakened, leading to a collective motion state which does not occur in the overdamped limit. A turbulent transition regime between the two states can be characterized by strong density fluctuations and the absence of global orderin
Keywords: active particles; mean field; inertia; non-equilibrium

Mean-intercept anisotropy analysis of porous media. I. Analytic formulae for anisotropic Boolean models - Klatt, Michael A.; Schroder-Turk, Gerd E.; Mecke, Klaus (Medical Physics, 2017)
Purpose Structure-property relations, which relate the shape of the microstructure to physical properties such as transport or mechanical properties, need sensitive measures of structure. What are suitable fabric tensors that quantify the shape of anisotropic heterogeneous materials? The mean intercept length is among the most commonly used characteristics of anisotropy in porous media, for example, of trabecular bone in medical physics. Methods We analyze the orientation-biased Boolean model, a versatile stochastic model that represents microstructures as overlapping grains with an orientation bias towards a preferred direction. This model is an extension of the isotropic Boolean model, which has been shown to truthfully reproduce multi-functional properties of isotropic porous media. We explain the close relationship between the concept of intersections with test lines to the elaborate mathematical theory of queues, and how explicit results from the latter can be directly applied to characterize microstructures. Results In this series of two papers, we provide analytic formulas for the anisotropic Boolean model and demonstrate often overlooked conceptual shortcomings of this approach. Queuing theory is used to derive simple and illustrative formulas for the mean intercept length. It separates into an intensity-dependent and an orientation-dependent factor. The global average of the mean intercept length can be expressed by local characteristics of a single grain alone. Conclusions We thus identify which shape information about the random process the mean intercept length contains. The connection between global and local quantities helps to interpret observations and provides insights into the possibilities and limitations of the analysis. In the second paper of this series, we discuss, based on the findings in this paper, short-comings of the mean intercept analysis for (bone-)microstructure characterization. We will suggest alternative and better defined sensitive anisotropy measures from integral geometry.
EAM Import::2019-03-12

Mean-intercept anisotropy analysis of porous media. II. Conceptual shortcomings of the MIL tensor definition and Minkowski tensors as an alternative - Klatt, Michael A.; Schroder-Turk, Gerd E.; Mecke, Klaus (Medical Physics, 2017)
Purpose Structure-property relations, which relate the shape of the microstructure to physical properties such as transport or mechanical properties, need sensitive measures of structure. What are suitable fabric tensors to quantify the shape of anisotropic heterogeneous materials? The mean intercept length is among the most commonly used characteristics of anisotropy in porous media, e.g., of trabecular bone in medical physics. Yet, in this series of two papers we demonstrate that it has conceptual shortcomings that limit the validity of its results. Methods We test the validity of general assumptions regarding the properties of the mean-intercept length tensor using analytical formulas for the mean-intercept lengths in anisotropic Boolean models (derived in part I of this series), augmented by numerical simulations. We discuss in detail the functional form of the mean intercept length as a function of the test line orientations. Results As the most prominent result, we find that, at least for the example of overlapping grains modeling porous media, the polar plot of the mean intercept length is in general not an ellipse and hence not represented by a second-rank tensor. This is in stark contrast to the common understanding that for a large collection of grains the mean intercept length figure averages to an ellipse. The standard mean intercept length tensor defined by a least-square fit of an ellipse is based on a model mismatch, which causes an intrinsic lack of accuracy. Conclusions Our analysis reveals several shortcomings of the mean intercept length tensor analysis that pose conceptual problems and limitations on the information content of this commonly used analysis method. We suggest the Minkowski tensors from integral geometry as alternative sensitive measures of anisotropy. The Minkowski tensors allow for a robust, comprehensive, and systematic approach to quantify various aspects of structural anisotropy. We show the Minkowski tensors to be more sensitive, in the sense, that they can quantify the remnant anisotropy of structures not captured by the mean intercept length analysis. If applied to porous tissue and microstructures, this improved structure characterization can yield new insights into the relationships between geometry and material properties.
EAM Import::2019-03-12

Measurement of atmospheric neutrino oscillations with the ANTARES neutrino telescope ANTARES Collaboration - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J. -J.; Baret, B.; Basa, S.; et al. (Physics Letters B, 2012)
The data taken with the ANTARES neutrino telescope from 2007 to 2010, a total live time of 863 days, are used to measure the oscillation parameters of atmospheric neutrinos. Muon tracks are reconstructed with energies as low as 20 GeV. Neutrino oscillations will cause a suppression of vertical upgoing muon neutrinos of such energies crossing the Earth. The parameters determining the oscillation of atmospheric neutrinos are extracted by fitting the event rate as a function of the ratio of the estimated neutrino energy and reconstructed flight path through the Earth. Measurement contours of the oscillation parameters in a two-flavour approximation are derived. Assuming maximal mixing, a mass difference of Delta m(32)(2) = (3.1 +/- 0.9) . 10(-3) eV(2) is obtained, in good agreement with the world average value. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Neutrino oscillations; Neutrino telescope; ANTARES

Measurement of the atmospheric nu (mu) energy spectrum from 100 GeV to 200 TeV with the ANTARES telescope - Adrian-Martinez, S.; Albert, A.; Al Samarai, I.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J. -J.; Baret, B.; Barrios-Marti, J.; et al. (European Physical Journal C, 2013)
Atmospheric neutrinos are produced during cascades initiated by the interaction of primary cosmic rays with air nuclei. In this paper, a measurement of the atmospheric energy spectrum in the energy range 0.1-200 TeV is presented, using data collected by the ANTARES underwater neutrino telescope from 2008 to 2011. Overall, the measured flux is similar to 25 % higher than predicted by the conventional neutrino flux, and compatible with the measurements reported in ice. The flux is compatible with a single power-law dependence with spectral index gamma (meas)=3.58 +/- 0.12. With the present statistics the contribution of prompt neutrinos cannot be established.

Measurement of the group velocity of light in sea water at the ANTARES site - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Jesus, A. C. Assis; Astraatmadja, T.; Aubert, J-J.; Baret, B.; et al. (Astroparticle Physics, 2012)
The group velocity of light has been measured at eight different wavelengths between 385 nm and 532 nm in the Mediterranean Sea at a depth of about 2.2 km with the ANTARES optical beacon systems. A parametrisation of the dependence of the refractive index on wavelength based on the salinity, pressure and temperature of the sea water at the ANTARES site is in good agreement with these measurements. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: ANTARES; Neutrino telescope; Optical beacon system; Velocity of light; Refractive index

Measuring fast stochastic displacements of bio-membranes with dynamic optical displacement spectroscopy - Monzel, Cornelia; Schmidt, Daniel; Kleusch, C.; Kirchenbuechler, D.; Seifert, U.; Smith, Ana-Suncana; Sengupta, Kheya; Merkel, Rudolf (Nature Communications, 2015)
Stochastic displacements or fluctuations of biological membranes are increasingly recognized as an important aspect of many physiological processes, but hitherto their precise quantification in living cells was limited due to a lack of tools to accurately record them. Here we introduce a novel technique-dynamic optical displacement spectroscopy (DODS), to measure stochastic displacements of membranes with unprecedented combined spatio-temporal resolution of 20 nm and 10 mu s. The technique was validated by measuring bending fluctuations of model membranes. DODS was then used to explore the fluctuations in human red blood cells, which showed an ATP-induced enhancement of non-Gaussian behaviour. Plasma membrane fluctuations of human macrophages were quantified to this accuracy for the first time. Stimulation with a cytokine enhanced non-Gaussian contributions to these fluctuations. Simplicity of implementation, and high accuracy make DODS a promising tool for comprehensive understanding of stochastic membrane processes.

Measuring holographic entanglement entropy on a quantum simulator - Li, Keren; Han, Muxin; Qu, Dongxue; Huang, Zichang; Long, Guilu; Wan, Yidun; Lu, Dawei; Zeng, Bei; Laflamme, Raymond (npj Quantum Information, 2019)
Quantum simulation promises to have wide applications in many fields where problems are hard to model with classical computers. Various quantum devices of different platforms have been built to tackle the problems in, say, quantum chemistry, condensed matter physics, and high-energy physics. Here, we report an experiment towards the simulation of quantum gravity by simulating the holographic entanglement entropy. On a six-qubit nuclear magnetic resonance quantum simulator, we demonstrate a key result of Anti-de Sitter/conformal field theory (AdS/CFT) correspondence-the Ryu-Takayanagi formula is demonstrated by measuring the relevant entanglement entropies on the perfect tensor state. The fidelity of our experimentally prepared the six-qubit state is 85.0% via full state tomography and reaches 93.7% if the signal-decay due to decoherence is taken into account. Our experiment serves as the basic module of simulating more complex tensor network states that exploring AdS/CFT correspondence. As the initial experimental attempt to study AdS/CFT via quantum information processing, our work opens up new avenues exploring quantum gravity phenomena on quantum simulators.
CRIS-Team WoS Importer:2019-05-14

Measuring the Invisible: Determining the Size of Growing Nanodomains Using the "Inverse FCS" - Fenz, Susanne F.; Smith, Ana-Suncana; Monzel, Cornelia (Biophysical Journal, 2017)
Molecular recruitment into functional domains in the cell plasma membrane is an important prerequisite for many cellular processes, such as cell signaling, cell-matrix adhesion, or the formation of synapses. High precision measurements of the origin and evolution of these structures is key to their understanding; however, experimental methods with which one can detect molecular dynamics and aggregation, with microsecond temporal resolution and at nanometer scales, are scarce.One of the most developed approaches, which is up to the task, is fluorescence correlation spectroscopy (FCS). In FCS, fluorescent particles diffuse through a laser excitation beam and emit pulses of light proportional to the particle brightness.One way to circumvent the issue of relating probe intensities to their number is to use inverse fluorescence correlation spectroscopy (iFCS). Here, as opposed to conventional FCS, the molecule of interest is not labeled but diffuses in a homogeneously fluorescent environment, giving rise to negative stochastic intensity fluctuations.
Keywords: fluorescence correlation spectroscoppy; membranes

Mechanical model for catch-bond-mediated cell adhesion in shear flow - Li, Long; Kang, Wei; Wang, Jizeng (International Journal of Molecular Sciences, 2020)
Catch bond, whose lifetime increases with applied tensile force, can often mediate rolling adhesion of cells in a hydrodynamic environment. However, the mechanical mechanism governing the kinetics of rolling adhesion of cells through catch-bond under shear flow is not yet clear. In this study, a mechanical model is proposed for catch-bond-mediated cell adhesion in shear flow. The stochastic reaction of bond formation and dissociation is described as a Markovian process, whereas the dynamic motion of cells follows classical analytical mechanics. The steady state of cells significantly depends on the shear rate of flow. The upper and lower critical shear rates required for cell detachment and attachment are extracted, respectively. When the shear rate increases from the lower threshold to the upper threshold, cell rolling became slower and more regular, implying the flow-enhanced adhesion phenomenon. Our results suggest that this flow-enhanced stability of rolling adhesion is attributed to the competition between stochastic reactions of bonds and dynamics of cell rolling, instead of force lengthening the lifetime of catch bonds, thereby challenging the current view in understanding the mechanism behind this flow-enhanced adhesion phenomenon. Moreover, the loading history of flow defining bistability of cell adhesion in shear flow is predicted. These theoretical predictions are verified by Monte Carlo simulations and are related to the experimental observations reported in literature.
CRIS-Team Scopus Importer:2020-02-04
Keywords: Bistability; Catch bond; Flow-enhanced adhesion; Markovian process; Rolling adhesion; Shear rate

Mechanical Regulation of Epithelial Tissue Homeostasis - Kaliman, Sara; Hubert, Maxime; Wollnik, Carina; Nuic, Lovro; Vurnek, Damir; Gehrer, Simone; Lovrić, Jakov; Dudziak, Diana; Rehfeldt, Florian; Smith, Ana-Suncana (Physical Review X, 2021)
Despite recent efforts to understand homeostasis in epithelial tissues, there are many unknowns surrounding this steady state. It is considered to be regulated by mechanoresponse, but unlike for single cells, this idea remains heavily debated for tissues. Here, we show that changes in matrix stiffness induce a nonequilibrium transition from tubular to squamous Madin-Darby Canine Kidney II tissues. Nonetheless, despite different cell morphologies and densities, all homeostatic tissues display equivalent topologies, which, hence, must be actively targeted and regulated. On the contrary, the mechanoresponse induces dramatic changes in the large-scale organization of the colonies. On stiff gels, this yields an unreported cooperative state of motile cells displaying higher densities than in the arrested homeostatic state, which suggests a more complex relation between cell density and motility than previously anticipated. Our results unequivocally relate the mechanosensitive properties of individual cells to the evolving macroscopic structures, an effect that could be important for understanding the emergent pathologies of living tissues.
CRIS-Team WoS Importer:2021-08-20

Mechanism of charge transfer/disproportionation in LnCu(3)Fe(4)O(12) (Ln = lanthanides) - Rezaei, N.; Hansmann, Philipp; Bahramy, M. S.; Arita, Ryotaro (Physical Review B, 2014)
The Fe-Cu intersite charge transfer and Fe charge disproportionation are interesting phenomena observed in some LnCu(3)Fe(4)O(12) (Ln = lanthanides) compounds containing light and heavy Ln atoms, respectively. We show that a change in the spin state is responsible for the intersite charge transfer in the light Ln compounds. At the high-spin state, such systems prefer an unusual Cu d(8) configuration, whereas at the low-spin state they retreat to the normal Cu d(9) configuration through a charge transfer from Fe to the Cu 3d(xy) orbital. We find that the strength of the crystal-field splitting and the relative energy ordering between Cu 3d(xy) and Fe 3d states are the key parameters determining the intersite charge transfer (charge disproportionation) in light (heavy) Ln compounds. It is further proposed that the size of Ln affects the on-site interaction strength of Cu 3d states, leading to a strong modification of the Cu L-3-edge spectrum, as observed by the x-ray-absorption spectroscopy.
CRIS-Team WoS Importer:2020-02-19

Mechanism of the Water–Gas Shift Reaction Catalyzed by Efficient Ruthenium-Based Catalysts: A Computational and Experimental Study - Stepic, Robert; Wick, Christian; Strobel, Vinzent; Berger, Daniel; Vucemilovic-Alagic, Natasa; Haumann, Marco; Wasserscheid, Peter; Smith, Ana-Suncana; Smith, David M. (Angewandte Chemie International Edition, 2019)
Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru-based, homogeneously catalyzed water-gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru-complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO) 3 Cl 3 ] − complex. Herein we present state-of-the-art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate-limiting step involves water is supported by using D 2 O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.
CRIS-Team Scopus Importer:2019-08-16
Keywords: ab initio calculations; reaction mechanisms; ruthenium; supported catalysts; water–gas shift reaction

Mechanisms for spin supersolidity in S=1/2 spin-dimer antiferromagnets - Picon, J. -D.; Albuquerque, A. F.; Schmidt, Kai Phillip; Laflorencie, Nicolas; Troyer, Matthias; Mila, F. (Physical Review B, 2008)
Using perturbative expansions and the contractor renormalization (CORE) algorithm, we obtain effective hard-core bosonic Hamiltonians describing the low-energy physics of S=1/2 spin-dimer antiferromagnets known to display supersolid phases under an applied magnetic field. The resulting effective models are investigated by means of mean-field analysis and quantum Monte Carlo simulations. A "leapfrog mechanism," through means of which extra singlets delocalize in a checkerboard-solid environment via correlated hoppings, is unveiled that accounts for the supersolid behavior.

Mechanistic Insight into Solution-Based Atomic Layer Deposition of CuSCN Provided by In Situ and Ex Situ Methods - Hilpert, Felix; Liao, Pei-Chun; Franz, Evanie; Koch, Vanessa; Fromm, Lukas; Topraksal, Ece; Görling, Andreas; Smith, Ana-Suncana; Barr, Maissa; Bachmann, Julien; Brummel, Olaf; Libuda, Jörg (ACS Applied Materials and Interfaces, 2023)
Solution-based atomic layer deposition (sALD) processes enable the preparation of thin films on nanostructured surfaces while controlling the film thickness down to a monolayer and preserving the homogeneity of the film. In sALD, a similar operation principle as in gas-phase ALD is used, however, with a broader range of accessible materials and without requiring expensive vacuum equipment. In this work, a sALD process was developed to prepare CuSCN on a Si substrate using the precursors CuOAc and LiSCN. The film growth was studied by ex situ atomic force microscopy (AFM), analyzed by a neural network (NN) approach, ellipsometry, and a newly developed in situ infrared (IR) spectroscopy experiment in combination with density functional theory (DFT). In the self-limiting sALD process, CuSCN grows on top of an initially formed two-dimensional (2D) layer as three-dimensional spherical nanoparticles with an average size of ∼25 nm and a narrow particle size distribution. With increasing cycle number, the particle density increases and larger particles form via Ostwald ripening and coalescence. The film grows preferentially in the β-CuSCN phase. Additionally, a small fraction of the α-CuSCN phase and defect sites form.<br
Keywords: solution atomic layer deposition; liquid phase; in situ IR spectroscopy; atomic force microscopy; copper thiocyanate; neural network; density functional theory

Membrane fluctuations mediate lateral interaction between cadherin bonds - Fenz, Susanne F.; Bihr, Timo; Schmidt, Daniel; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Nature Physics, 2017)
The integrity of living tissues is maintained by adhesion domains of trans-bonds formed between cadherin proteins residing on opposing membranes of neighbouring cells. These domains are stabilized by lateral cis-interactions between the cadherins on the same cell. However, the origin of cis-interactions remains perplexing since they are detected only in the context of trans-bonds. By combining experimental, analytical and computational approaches, we identify bending fluctuations of membranes as a source of long-range cis-interactions, and a regulator of trans-interactions. Specifically, nanometric membrane bending and fluctuations introduce cooperative effects that modulate the affinity and binding/unbinding rates for trans-dimerization, dramatically affecting the nucleation and growth of adhesion domains. Importantly, this regulation relies on physical principles and not on details of protein-protein interactions. These omnipresent fluctuations can thus act as a generic control mechanism in all types of cell adhesion, suggesting a hitherto unknown physiological role for recently identified active fluctuations of cellular membranes.
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; ADHERENS JUNCTIONS; GIANT VESICLES; I CADHERINS; BINDING; DYNAMICS; DOMAINS; ACTIN; SPECIFICITY

Memory truncated Kadanoff-Baym equations - Stahl, Christopher; Dasari, Nagamalleswara Rao; Li, Jiajun; Picano, Antonio; Werner, Philipp; Eckstein, Martin (Physical Review B, 2022)
The Keldysh formalism for nonequilibrium Green's functions is a powerful theoretical framework for the description of the electronic structure, spectroscopy, and dynamics of strongly correlated systems. However, the underlying Kadanoff-Baym equations (KBE) for the two-time Keldysh Green's functions involve a memory kernel, which results in a high computational cost for long simulation times tmax, with a cubic scaling of the computation time with tmax. Truncation of the memory kernel can reduce the computational cost to linear scaling with tmax, but the required memory times will depend on the model and the diagrammatic approximation to the self-energy. We explain how a truncation of the memory kernel can be incorporated into the time-propagation algorithm to solve the KBE, and investigate the systematic truncation of the memory kernel for the Hubbard model in different parameter regimes, and for different diagrammatic approximations. The truncation is easier to control within dynamical mean-field solutions, where it is applied to a momentum-independent self-energy. Here, simulation times up to two orders of magnitude longer are accessible both in the weak and strong coupling regime, allowing for a study of long-time phenomena such as the crossover between prethermalization and thermalization dynamics.
CRIS-Team Scopus Importer:2022-04-22

Metasurface-Based Hybrid Optical Cavities for Chiral Sensing - Baßler, Nico S.; Aiello, Andrea; Schmidt, Kai Phillip; Genes, Claudiu; Reitz, Michael (Physical Review Letters, 2024)
Quantum metasurfaces, i.e., two-dimensional subwavelength arrays of quantum emitters, can be employed as mirrors towards the design of hybrid cavities, where the optical response is given by the interplay of a cavity-confined field and the surface modes supported by the arrays. We show that stacked layers of quantum metasurfaces with orthogonal dipole orientation can serve as helicity-preserving cavities. These structures exhibit ultranarrow resonances and can enhance the intensity of the incoming field by orders of magnitude, while simultaneously preserving the handedness of the field circulating inside the resonator, as opposed to conventional cavities. The rapid phase shift in the cavity transmission around the resonance can be exploited for the sensitive detection of chiral scatterers passing through the cavity. We discuss possible applications of these resonators as sensors for the discrimination of chiral molecules. Our approach describes a new way of chiral sensing via the measurement of particle-induced phase shifts.
CRIS-Team Scopus Importer:2024-02-09

Microlocal spectrum condition and Hadamard form for vector-valued quantum fields in curved spacetime - Sahlmann, Hanno; Verch, Rainer (Reviews in Mathematical Physics, 2001)
Some years ago, Radzikowski has found a characterization of Hadamard states for scalar quantum fields on a four-dimensional globally hyperbolic spacetime in terms of a specific form of the wavefront set of their two-point functions (termed "wavefront set spectrum condition"), thereby initiating a major progress in the understanding of Hadamard states and the further development of quantum field theory in curved spacetime. In the present work, we extend this important result on the equivalence of the wavefront set spectrum condition with the Hadamard condition from scalar fields to vector fields (sections in a vector bundle) which are subject to a wave-equation and are quantized so as to fulfill the covariant canonical commutation relations, or which obey a Dirac equation and are quantized according to the covariant anti-commutation relations, in any globally hyperbolic spacetime having dimension three or higher. In proving this result, a gap which is present in the published proof for the scalar field case will be removed. Moreover we determine the short-distance scaling limits of Hadamard states for vector-bundle valued fields, finding them to coincide with the corresponding flat-space, massless vacuum states.

Micropatterned Down-Converting Coating for White Bio-Hybrid Light-Emitting Diodes - Niklaus, Lukas; Tansaz, Samira; Dakhil, Haider; Weber, Katharina; Pröschel, Marlene; Lang, Martina; Kostrzewa, Monika Maria; Coto, Pedro B.; Detsch, Rainer; Sonnewald, Uwe; Wierschem, Andreas; Boccaccini, Aldo R.; et al. (Advanced Functional Materials, 2017)
White hybrid light-emitting diodes (WHLEDs) are considered as a solid approach toward environmentally sustainable lighting sources that meet the "Green Photonics" requirements. Here, WHLEDs with protein-based down-converting coatings, i.e., Bio-WHLEDs, are demonstrated and exhibit worthy white color quality, luminous efficiency, and stability values. The coatings feature a multilayered cascade-like architecture with thicknesses of 1-3 mm. This limits the efficiency due to the low optical transmittance. Thus, submillimeter coatings, where the location of the proteins is well-defined, are highly desired. It is in this context where the thrust of this work sets in. Here, a straightforward way to design microstructured single-layer coatings, in which the proteins are placed at our command by using 3D printing, is presented. Based on comprehensive spectroscopic and rheological investigations, the optimization of the matrix and the plotting to prepare different micropatterns, i.e., lines, open-grids, and closed-grids, is rationalized. The latter are applied to prepare Bio-WHLEDs with approximate to 5-fold enhancement of the luminous efficiency compared to the reference devices with a cascade-like coating, without losing stability and color quality. As such, this work shows a new route to exploit proteins for optoelectronics, setting a new avenue of research into the emerging field of Bio-WHLEDs.

Microscopic mechanism for the 1/8 magnetization plateau in SrCu2(BO3)(2) - Nemec, M.; Foltin, G. R.; Schmidt, Kai Phillip (Physical Review B, 2012)
The frustrated quantum magnet SrCu2(BO3)(2) shows a remarkably rich phase diagram in an external magnetic field including a sequence of magnetization plateaux. The by far experimentally most studied and most prominent magnetization plateau is the 1/8 plateau. Theoretically, one expects that this material is well described by the Shastry-Sutherland model. But, recent microscopic calculations indicate that the 1/8 plateau is energetically not favored. Here, we report on a very simple microscopic mechanism which naturally leads to a 1/8 plateau for realistic values of the magnetic exchange constants. We show that the 1/8 plateau with a square unit cell benefits most compared to other plateau structures from quantum fluctuations which, to a large part, are induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings result in kinetic terms in an effective hard-core-boson description leading to a renormalization of the energy of the different plateau structures which we treat in this work on the mean-field level. The stability of the resulting plateaux are discussed. Furthermore, our results indicate a series of stripe structures above 1/8 and a stable magnetization plateau at 1/6. Most qualitative aspects of our microscopic theory agree well with a recently formulated phenomenological theory for the experimental data of SrCu2(BO3)(2). Interestingly, our calculations point to a rather large ratio of the magnetic couplings in the Shastry-Sutherland model such that nonperturbative effects become essential for the understanding of the frustrated quantum magnet SrCu2(BO3)(2).

Microscopic theory for interface fluctuations in binary liquid mixtures - Mecke, Klaus; et al. (Journal of Chemical Physics, 2006)
Thermally excited capillary waves at fluid interfaces in binary liquid mixtures exhibit simultaneously both density and composition fluctuations. Based on a density functional theory for inhomogeneous binary liquid mixtures we derive an effective wavelength dependent Hamiltonian for fluid interfaces in these systems beyond the standard capillary-wave model. Explicit expressions are obtained for the surface tension, the bending rigidities, and the coupling constants of compositional capillary waves in terms of the profiles of the two number densities characterizing the mixture. These results lead to predictions for grazing-incidence x-ray scattering experiments at such interfaces. (c) 2006 American Institute of Physics.

Miniature chiral beamsplitter based on gyroid photonic crystals - Turner, Mark D.; Saba, Matthias; Zhang, Qiming; Cumming, Benjamin P.; Schröder-Turk, Gerd; Gu, Min (Nature Photonics, 2013)
The linearly polarizing beamsplitter is a widely used optical component in photonics. It is typically built from a linearly birefringent crystal such as calcite, which has different critical reflection angles for s- and p-polarized light, leading to the transmission of one linear polarization and angled reflection of the other. However, the analogue for splitting circularly polarized light has yet to be demonstrated due to a lack of natural materials with sufficient circular birefringence. Here, we present a nano-engineered photonic-crystal chiral beamsplitter that fulfils this task. It consists of a prism featuring a nanoscale chiral gyroid network and can separate left- and right-handed circularly polarized light in the wavelength region around 1.615 µm. The structure is fabricated using a galvo-dithered direct laser writing method and could become a useful component for developing integrated photonic circuits that provide a new form of polarization control.
EAM Import::2019-03-12

Minimal surface scaffold designs for tissue engineering - Kapfer, Sebastian; Hyde, Stephen T.; Mecke, Klaus; Arns, Christoph H.; Schröder-Turk, Gerd (Biomaterials, 2011)
Triply-periodic minimal surfaces are shown to be a more versatile source of biomorphic scaffold designs than currently reported in the tissue engineering literature. A scaffold architecture with sheetlike morphology based on minimal surfaces is discussed, with significant structural and mechanical advantages over conventional designs. These sheet solids are porous solids obtained by inflation of cubic minimal surfaces to sheets of finite thickness, as opposed to the conventional network solids where the minimal surface forms the solid/void interface. Using a finite-element approach, the mechanical stiffness of sheet solids is shown to exceed that of conventional network solids for a wide range of volume fractions and material parameters. We further discuss structure property relationships for mechanical properties useful for custom-designed fabrication by rapid prototyping. Transport properties of the scaffolds are analyzed using Lattice-Boltzmann computations of the fluid permeability. The large number of different minimal surfaces, each of which can be realized as sheet or network solids and at different volume fractions, provides design flexibility essential for the optimization of competing design targets. (C) 2011 Elsevier Ltd. All rights reserved.
Keywords: Bone tissue engineering; Finite element analysis; Mechanical properties; Scaffold; Rapid prototyping

Minimal surfaces in nuclear pasta with the time-dependent hartree-fock approach - Schuetrumpf, Bastian; Klatt, Michael; Iida, K.; Schröder-Turk, Gerd; Maruhn, J. A.; Mecke, Klaus; Reinhard, Paul-Gerhard (Proceedings of Science, 2014)
In continuation to the studies of the whole variety of pasta shapes in [1], we present here calculations performed with the Hartree-Fock and time-dependent Hartree- Fock method concerning the mid-density range of pasta shapes: The slab-like, connected rod-like (p-surface) and the gyroidal shapes. On the one hand we present simulations of the dynamic formation of these shapes at finite temperature. On the other hand we calculate the binding energies of these shapes for varying simulation box lengths and mean densities. All of these shapes are found to be at least metastable. The slab shape has a slightly lower energy because of the lack of curvature, but among these three configurations the gyroidal shape is metastable for the widest range in mean density.
CRIS-Team Scopus Importer:2023-07-24

Minkowski tensor density formulas for Boolean models - Hoerrmann, Julia; Hug, Daniel; Klatt, Michael; Mecke, Klaus (Advances in Applied Mathematics, 2014)
A stationary Boolean model is the union set of random compact particles which are attached to the points of a stationary Poisson point process. For a stationary Boolean model with convex grains we consider a recently developed collection of shape descriptors, the so called Minkowski tensors. By combining spatial and probabilistic averaging we define Minkowski tensor densities of a Boolean model. These densities are global characteristics of the union set which can be estimated from observations. In contrast local characteristics like the mean Minkowski tensor of a single random particle cannot be observed directly, since the particles overlap. We relate the global to the local properties by density formulas for the Minkowski tensors. These density formulas generalize the well known formulas for intrinsic volume densities and are obtained by applying results from translative integral geometry. Our results support the idea that the degree of anisotropy of a Boolean model may be expressed in terms of the Minkowski tensor densities. Furthermore we observe that for smooth grains the mean curvature radius function of a particle can be reconstructed. from the Minkowski tensor densities. In a simulation study we numerically determine Minkowski tensor densities for nonisotropic Boolean models based on ellipses and on rectangles in two dimensions and find excellent agreement with the derived analytic density formulas. The tensor densities can be used to characterize the orientational distribution of the grains and to estimate model parameters for non-isotropic distributions. In particular, the numerically determined values for the density of the Euler characteristic allow the estimation of certain mixed functionals of the grains. (C) 2014 Elsevier Inc. All rights reserved.
Keywords: Stochastic geometry; Boolean model; Stationarity; Anisotropy; Minkowski tensors; Poisson process; Translative integral geometry

Minkowski Tensor Shape Analysis of Cellular, Granular and Porous Structures - Peukert, Wolfgang; Schröder-Turk, Gerd; Mickel, Walter; Kapfer, Sebastian; Klatt, Michael; Schaller, Fabian; Hoffmann, Matthias; Kleppmann, Nicola; Inayat, Amer; Armstrong, Patrick; Hug, Daniel; Reichelsdorfer, Martin; et al. (Advanced Materials, 2011)
Predicting physical properties of materials with spatially complex structures is one of the most challenging problems in material science. One key to a better understanding of such materials is the geometric characterization of their spatial structure. Minkowski tensors are tensorial shape indices that allow quantitative characterization of the anisotropy of complex materials and are particularly well suited for developing structure-property relationships for tensor-valued or orientation-dependent physical properties. They are fundamental shape indices, in some sense being the simplest generalization of the concepts of volume, surface and integral curvatures to tensor-valued quantities. Minkowski tensors are based on a solid mathematical foundation provided by integral and stochastic geometry, and are endowed with strong robustness and completeness theorems. The versatile definition of Minkowski tensors applies widely to different types of morphologies, including ordered and disordered structures. Fast linear-time algorithms are available for their computation. This article provides a practical overview of the different uses of Minkowski tensors to extract quantitative physically-relevant spatial structure information from experimental and simulated data, both in 2D and 3D. Applications are presented that quantify (a) alignment of co-polymer films by an electric field imaged by surface force microscopy; (b) local cell anisotropy of spherical bead pack models for granular matter and of closed-cell liquid foam models; (c) surface orientation in open-cell solid foams studied by X-ray tomography; and (d) defect densities and locations in molecular dynamics simulations of crystalline coppe
Keywords: geometric; statistic; spatial; anisotropy; shape; morphology; crystal

Minkowski tensors of anisotropic spatial structure - Schröder-Turk, Gerd; Mickel, W.; Kapfer, Sebastian; Schaller, Fabian; Breidenbach, B.; Hug, Daniel; Mecke, Klaus (New Journal of Physics, 2013)
This paper describes the theoretical foundation of and explicit algorithms for a novel approach to morphology and anisotropy analysis of complex spatial structure using tensor-valued Minkowski functionals, the so-called Minkowski tensors. Minkowski tensors are generalizations of the well-known scalar Minkowski functionals and are explicitly sensitive to anisotropic aspects of morphology, relevant for example for elastic moduli or permeability of microstructured materials. Here we derive explicit linear-time algorithms to compute these tensorial measures for three-dimensional shapes. These apply to representations of any object that can be represented by a triangulation of its bounding surface; their application is illustrated for the polyhedral Voronoi cellular complexes of jammed sphere configurations and for triangulations of a biopolymer fibre network obtained by confocal microscopy. The paper further bridges the substantial notational and conceptual gap between the different but equivalent approaches to scalar or tensorial Minkowski functionals in mathematics and in physics, hence making the mathematical measure theoretic formalism more readily accessible for future application in the physical sciences.

Misfits in skyrme-hartree-fock - Erler, J.; Klüpfel, P.; Reinhard, Paul-Gerhard (Journal of Physics G: Nuclear and Particle Physics, 2010)
We address very briefly five critical points in the context of the Skyrme-Hartree-Fock (SHF) scheme: (1) the impossibility of considering it as an interaction, (2) a possible inconsistency of correlation corrections such as, e.g., the centre-of-mass correction, (3) problems of describing the giant dipole resonance (GDR) simultaneously in light and heavy nuclei, (4) deficiencies in the extrapolation of binding energies to super-heavy elements (SHE) and (5) a yet inappropriate trend in fission lifetimes when going to the heaviest SHE. While the first two points have a more formal bias, the other three points have practical implications and wait for solution. © 2010 IOP Publishing Ltd.
CRIS-Team Scopus Importer:2023-07-24

Mixing properties of bi-disperse ellipsoid assemblies: mean-field behaviour in a granular matter experiment - Schaller, Fabian; Punzmann, H.; Schröder-Turk, G. E.; Saadatfar, M. (Soft Matter, 2023)
The structure and spatial statistical properties of amorphous ellipsoid assemblies have profound scientific and industrial significance in many systems, from cell assays to granular materials. This paper uses a fundamental theoretical relationship for mixture distributions to explain the observations of an extensive X-ray computed tomography study of granular ellipsoidal packings. We study a size-bi-disperse mixture of two types of ellipsoids of revolutions that have the same aspect ratio of α ≈ 0.57 and differ in size, by about 10% in linear dimension, and compare these to mono-disperse systems of ellipsoids with the same aspect ratio. Jammed configurations with a range of packing densities are achieved by employing different tapping protocols. We numerically interrogate the final packing configurations by analyses of the local packing fraction distributions calculated from the Voronoi diagrams. Our main finding is that the bi-disperse ellipsoidal packings studied here can be interpreted as a mixture of two uncorrelated mono-disperse packings, insensitive to the compaction protocol. Our results are consolidated by showing that the local packing fraction shows no correlation beyond their first shell of neighbours in the binary mixtures. We propose a model of uncorrelated binary mixture distribution that describes the observed experimental data with high accuracy. This analysis framework will enable future studies to test whether the observed mean-field behaviour is specific to the particular granular system or the specific parameter values studied here or if it is observed more broadly in other bi-disperse non-spherical particle systems.
CRIS-Team Scopus Importer:2023-01-27

Mode-coupling theory of the glass transition for confined fluids - Lang, Simon; Schilling, Rolf; Krakoviack, Vincent; Franosch, Thomas (Physical Review E, 2012)
We present a detailed derivation of a microscopic theory for the glass transition of a liquid enclosed between two parallel walls relying on a mode-coupling approximation. This geometry lacks translational invariance perpendicular to the walls, which implies that the density profile and the density-density correlation function depends explicitly on the distances to the walls. We discuss the residual symmetry properties in slab geometry and introduce a symmetry adapted complete set of two-point correlation functions. Since the currents naturally split into components parallel and perpendicular to the walls the mathematical structure of the theory differs from the established mode-coupling equations in bulk. We prove that the equations for the nonergodicity parameters still display a covariance property similar to bulk liquids.
EAM Import::2019-03-12

Modeling charge transport in C60-based self-assembled monolayers for applications in field-effect transistors - Leitherer, Susanne; Jäger, Christof; Halik, Marcus; Clark, Timothy; Thoss, Michael (Journal of Chemical Physics, 2014)
We have investigated the conductance properties of C60-containing self-assembled monolayers (SAMs), which are used in organic field-effect transistors, employing a combination of molecular-dynamics simulations, semiempirical electronic structure calculations, and Landauer transport theory. The results reveal the close relation between the transport characteristics and the structural and electronic properties of the SAM. Furthermore, both local pathways of charge transport in the SAMs and the influence of structural fluctuations are analyzed.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.ITP.ppem.modeli

Modeling of the deposition of Na Clusters on MgO(001) - Bär, M.; Dinh, P. M.; Moskaleva, L. V.; Reinhard, Paul-Gerhard; Rösch, N.; Suraud, E. (Physical Review B - Condensed Matter and Materials Physics, 2009)
We investigate the dynamics of deposition of small Na clusters on MgO(001) surface. A hierarchical modeling is used combining quantum mechanical with molecular mechanical description. Full time-dependent density-functional theory is used for the cluster electrons while the substrate atoms are treated at a classical level. We consider Na6 and Na8 at various impact energies. We analyze the dependence on cluster geometry, trends with impact energy, and energy balance. We compare the results with deposit on the much softer Ar(001) surface. © 2009 The American Physical Society.
CRIS-Team Scopus Importer:2023-07-24

Modelling diffusive transport of particles interacting with slit nanopore walls: The case of fullerenes in toluene filled alumina pores - Baer, Andreas; Malgaretti, Paolo; Kaspereit, Malte; Harting, Jens; Smith, Ana-Suncana (Journal of Molecular Liquids, 2022)

Molecular biomechanics controls protein mixing and segregation in adherent membranes - Li, Long; Stumpf, Bernd Henning; Smith, Ana-Suncana (International Journal of Molecular Sciences, 2021)
Cells interact with their environment by forming complex structures involving a mul-titude of proteins within assemblies in the plasma membrane. Despite the omnipresence of these assemblies, a number of questions about the correlations between the organisation of domains and the biomechanical properties of the involved proteins, namely their length, flexibility and affinity, as well as about the coupling to the elastic, fluctuating membrane, remain open. Here we address these issues by developing an effective Kinetic Monte Carlo simulation to model membrane adhesion. We apply this model to a typical experiment in which a cell binds to a functionalized solid supported bilayer and use two ligand-receptor pairs to study these couplings. We find that differences in affinity and length of proteins forming adhesive contacts result in several characteristic features in the calculated phase diagrams. One such feature is mixed states occurring even with proteins with length differences of 10 nm. Another feature are stable nanodomains with segregated proteins appearing on time scales of cell experiments, and for biologically relevant parameters. Furthermore, we show that macroscopic ring-like patterns can spontaneously form as a consequence of emergent protein fluxes. The capacity to form domains is captured by an order parameter that is founded on the virial coefficients for the membrane mediated interactions between bonds, which allow us to collapse all the data. These findings show that taking into account the role of the membrane allows us to recover a number of experimentally observed patterns. This is an important perspective in the context of explicit biological systems, which can now be studied in significant detail.
CRIS-Team Scopus Importer:2021-04-19
Keywords: Adhesive contact; Membrane adhesion; Nanodomain; Phase space; Protein biomechanics; Receptor-ligand pairs

Molecular-scale spatio-chemical control of the activating-inhibitory signal integration in NK cells - Toledo, Esti; Le Saux, Guillaume; Edri, Avishay; Li, Long; Rosenberg, Maor; Keidar, Yossi; Bhingardive, Viraj; Radinsky, Olga; Hadad, Uzi; Di Primo, Carmelo; Buffeteau, Thierry; Smith, Ana-Suncana; et al. (Science Advances, 2021)
The role of juxtaposition of activating and inhibitory receptors in signal inhibition of cytotoxic lymphocytes remains strongly debated. The challenge lies in the lack of tools that allow simultaneous spatial manipulation of signaling molecules. To circumvent this, we produced a nanoengineered multifunctional platform with molecular-scale spatial control of ligands, which was applied to elucidate KIR2DL1-mediated inhibition of NKG2D signaling - receptors of natural killer cells. This platform was conceived by bimetallic nanodot patterning with molecular-scale registry, followed by a ternary functionalization with distinct moieties. We found that a 40-nm gap between activating and inhibitory ligands provided optimal inhibitory conditions. Supported by theoretical modeling, we interpret these findings as a consequence of the size mismatch and conformational flexibility of ligands in their spatial interaction. This highly versatile approach provides an important insight into the spatial mechanism of inhibitory immune checkpoints, which is essential for the rational design of future immunotherapies.
CRIS-Team Scopus Importer:2021-07-02

Molecular Transistor Controlled through Proton Transfer - Weckbecker, Dominik; Coto, P. B.; Thoss, M. (Journal of Physical Chemistry Letters, 2021)
The potential of proton transfer reactions as a fundamental mechanism to realize a nanoscale molecular transistor is investigated. Employing density functional theory and the nonequilibrium Green's function formalism, we identify molecule-graphene nanojunctions, which exhibit high- and low-conducting states depending on the specific location of protons in the molecular bridge. In addition, we show that an electrostatic gate field can control the proton transfer process and thus allow specific conductance states to be selected. In this way, the current in the junction can be switched on and off as in a field-effect transistor. The underlying mechanism is analyzed in detail.
CRIS-Team Scopus Importer:2021-01-15

Momentum-dependent relaxation dynamics of the doped repulsive Hubbard model - Sayyad, Sharareh; Tsuji, Naoto; Vaezi, Abolhassan; Capone, Massimo; Eckstein, Martin; Aoki, Hideo (Physical Review B, 2019)
We study the dynamical behavior of doped electronic systems subject to a global ramp of the repulsive Hubbard interaction. We start with formulating a real-time generalization of the fluctuation-exchange approximation. Implementing this numerically, we investigate the weak-coupling regime of the Hubbard model both in the electron-doped and hole-doped regimes. The results show that both local and nonlocal (momentum-dependent) observables evolve toward a thermal state, although the temperature of the final state depends on the ramp duration and the band filling. We further reveal a momentum-dependent relaxation rate of the distribution function in doped systems and trace back its physical origin to the anisotropic self-energies in the momentum space.
CRIS-Team WoS Importer:2019-05-03

Momentum-resolved spin-conserving two-triplon bound state and continuum in a cuprate ladder - Tseng, Yi; Paris, Eugenio; Schmidt, Kai Phillip; Zhang, Wenliang; Asmara, Teguh Citra; Bag, Rabindranath; Strocov, Vladimir N.; Singh, Surjeet; Schlappa, Justine; Rønnow, Henrik M.; Schmitt, Thorsten (Communications Physics, 2023)
Studying multi-particle elementary excitations has provided unique access to understand collective many-body phenomena in correlated electronic materials, paving the way towards constructing microscopic models. In this work, we perform O K-edge resonant inelastic X-ray scattering (RIXS) on the quasi-one-dimensional cuprate Sr 14Cu 24O 41 with weakly-doped spin ladders. The RIXS signal is dominated by a dispersing sharp mode 270 meV on top of a damped incoherent component 400-500 meV. Comparing with model calculations using the perturbative continuous unitary transformations method, the two components resemble the spin-conserving ΔS = 0 two-triplon bound state and continuum excitations in the spin ladders. Such multi-spin response with long-lived ΔS = 0 excitons is central to several exotic magnetic properties featuring Majorana fermions, yet remains unexplored given the generally weak cross-section with other experimental techniques. By investigating a simple spin-ladder model system, our study provides valuable insight into low-dimensional quantum magnetism.
CRIS-Team Scopus Importer:2023-06-30

Monte Carlo simulations of confined hard sphere fluids - Schröder-Turk, Gerd; Kuczera, S.; Hoerndlein, D.; Krach, Florian; Hiester, T.; Mecke, Klaus (Physics Procedia, 2010)
We describe a grand-canonical Monte Carlo simulation of a hard sphere fluid confined to porous media with arbitrary pore shape. The pore geometry is given by a triangulated surface representation of the solid-void interface. This algorithm is developed to study the dependence of thermodynamic quantities, such as the average density and adsorption, on the shape of the pore. Particular pore shape geometries that are analysed are the labyrinthine domains bounded by so-called triply-periodic minimal surfaces.
EAM Import::2019-03-12

Morphological characterization of patterns in reaction-diffusion systems - Mecke, Klaus (Physical Review E, 1996)
Morphological measures for spatial patterns occuring as dissipative structures in systems driven far from equilibrium are introduced. They characterize the geometry and topology of the patterns and are capable to distinguish irregular structures with respect to the morphology. In particular, we analyze turbulent and regular patterns (Turing patterns) in chemical reaction-diffusion systems observed in a tyro-dimensional open gel reactor with a chlorite-iodide-malonic acid reaction. Introducing the concept of level contours, the measures turn out to be polynomials of low order (cubic and fourth degree) in the grey-scale level of the images. Thus the dependence on the experimental conditions is reflected only in a finite number of coefficients, which can be used as order parameters for the morphology of patterns. We observe a symmetry breaking of the polynomials when the type of the pattern changes from hexagons to turbulence or stripes. Therefore it is possible to describe the pattern transitions quantitatively and it may be possible to classify them in a similar way like thermodynamic phase transitions.

Morphological characterization of point patterns - Mecke, Klaus; et al. (Biometrical Journal, 2005)
The paper describes the statistical estimation of the new characteristics. Some examples illustrate their application in the exploratory analysis of point patterns of tree positions in forests, in comparison to results obtained by means of second-order and distance characteristics.
Keywords: distance characteristic; Euler characteristic; forest; integral geometry; point process; second-order characteristic; statistical estimation

Morphological characterization of spinodal decomposition kinetics - Mecke, Klaus; et al. (European Physical Journal B, 1999)
The time evolution of the morphology of homogeneous phases during spinodal decomposition is described using a family of morphological measures known as Minkowski functionals. They provide the characteristic length scale L of patterns in a convenient, statistically robust, and computationally inexpensive way. They also allow one to study the scaling behavior of the content, shape, and connectivity of spatial structures and to define the crossover from the early stage decomposition to the late stage domain growth. We observe the scaling behavior L similar to t(alpha) with alpha = 2/3, alpha = 1/2, and alpha = 1/3 depending on the viscosity of the fluid. When approaching the spinodal density psp: we recover the prediction L similar to (rho - rho(sp))(-1/2) for the early time spinodal decomposition.

Morphological fluctuations of large-scale structure: The PSCz survey - Mecke, Klaus; et al. (Astronomy & Astrophysics, 2001)
In a follow-up study to a previous analysis of the IRAS 1.2 Jy catalogue, we quantify the morphological fluctuations in the PSCz survey. We use a variety of measures, among them the family of scalar Minkowski functionals. We confirm the existence of significant fluctuations that are discernible in volume-limited samples out to 200h(-1) Mpc. In contrast to earlier findings, comparisons with cosmological N-body simulations reveal that the observed fluctuations roughly agree with the cosmic variance found in corresponding mock samples. While two-point measures, e.g. the variance of count-in-cells, fluctuate only mildly, the fluctuations in the morphology on large scales indicate the presence of coherent structures that are at least as large as the sample.
Keywords: large-scale structure of Universe; cosmology : observation; galaxies : statistics

Morphological thermodynamics of composite media - Mecke, Klaus (ELSEVIER SCIENCE BV, 1998)
The homogeneous spatial domains of phases on a mesoscopic scale are a characteristic feature of many composite media such as complex fluids or porous materials. The thermodynamics and bulk properties of such composite media depend often on the morphology of its constituents, i.e., on the spatial structure of the homogeneous domains. Therefore, a statistical theory should include morphological descriptors to characterize the size, shape and connectivity of the aggregating mesophases. We propose a new model for studying composite media using morphological measures to describe the homogeneous spatial domains of the constituents. Under rather natural assumptions a general expression for the Hamiltonian can be given by extending the model of Widom and Rowlinson [B. Widom, J.S. Rowlinson, J. Chem. Phys. 52 (1970) 1670-1684] for penetrable spheres. The Hamiltonian includes energy contributions related to the volume, surface area, mean curvature, and Euler characteristic of the configuration generated by overlapping sets of arbitrary shapes. A general expression for the free energy of composite media is derived and we find that the Euler characteristic stabilizes a highly connected bicontinuous structure resembling the middle-phase in oil-water microemulsions for instance. (C) 1998 Elsevier Science B.V. All rights reserved.
Keywords: statistical mechanics; equation of state; penetrable spheres; integral geometry; Euler characteristic; microemulsion

Morphological thermodynamics of fluids: Shape dependence of free energies - Mecke, Klaus; et al. (Physical Review Letters, 2004)
We examine the dependence of a thermodynamic potential of a fluid on the geometry of its container. If motion invariance, continuity, and additivity of the potential are satisfied, only four morphometric measures are needed to describe fully the influence of an arbitrarily shaped container on the fluid. These three constraints can be understood as a more precise definition for the conventional term extensive and have as a consequence that the surface tension and other thermodynamic quantities contain, aside from a constant term, only contributions linear in the mean and Gaussian curvature of the container and not an infinite number of curvatures as generally assumed before. We verify this numerically in the entropic system of hard spheres bounded by a curved wall.

Morphology and Linear-Elastic Moduli of Random Network Solids - Nachtrab, Susan; Kapfer, Sebastian; Arns, Christoph H.; Madadi, Mahyar; Mecke, Klaus; Schröder-Turk, Gerd (Advanced Materials, 2011)
The dependence of linear-elastic properties on effective density is studied for porous network solids, by voxel-based finite element methods. The same dependence is found for solid structures derived from Poisson-Voronoi processes and from confocal microscopy images of collagen scaffolds. We recover the power-law for the bulk modulus for low densities and suggest a functional form for the cross-over to a high-density porous solid.

Morphology as indicator of adaptive changes of model tissues in osmotically and chemically changing environments - Höllring, Kevin; Vurnek, Damir; Gehrer, Simone; Dudziak, Diana; Hubert, Maxime; Smith, Ana-Suncana (Biomaterials Advances, 2023)
We investigate the formation and maintenance of the homeostatic state in the case of 2D epithelial tissues following an induction of hyperosmotic conditions, using media enriched with 80 to 320 mOsm of mannitol, NaCl, and urea. We characterise the changes in the tissue immediately after the osmotic shock, and follow it until the new homeostatic state is formed. We characterise changes in cooperative motility and proliferation pressure in the tissue upon treatment with the help of a theoretical model based on the delayed Fisher-Kolmogorov formalism, where the delay in density evolution is induced by the the finite time of the cell division. Finally we explore the adaptation of the homeostatic tissue to highly elevated osmotic conditions by evaluating the morphology and topology of cells after 20 days in incubation. We find that hyperosmotic environments together with changes in the extracellular matrix induce different mechanical states in viable tissues, where only some remain functional. The perspective is a relation between tissue topology and function, which could be explored beyond the scope of this manuscript. Experimental investigation of morphological effect of change of osmotic conditions on long-term tissue morphology and topology Effect of osmotic changes on transient tissue growth behaviour Analysis of recovery process of tissues post-osmotic-shock Toxicity limits of osmolytes in mid- to long-term tissue evolution Tissue adaptation to physiological changes in environment Long-term tissue stabilisation under altered osmotic conditions.
CRIS-Team Scopus Importer:2023-11-03
Keywords: Epithelium topology and morphology; Fisher-Kolmogorov theory; Hyperosmotic conditions; Model tissue development; Tissue adaptation

Morphology dependent interaction between Co(ii)-tetraphenylporphyrin and the MgO(100) surface - Ninova, Silviya; Malcıoğlu, Osman Barış; Auburger, Philipp; Franke, Matthias; Lytken, Ole; Steinrück, Hans-Peter; Bockstedte, Michel (Physical Chemistry Chemical Physics, 2021)
Porphyrins are key elements in organic-inorganic hybrid systems for a wide range of applications. Understanding their interaction with the substrate gives a handle on structural and electronic device properties. Here we investigate a single transition-metal porphyrin, namely Co(ii)-tetraphenylporphyrin (CoTPP), on the MgO(100) surface and the effect of multilayer film formation within hybrid density-functional theory and many-body perturbation theory. We focus on the relevant adsorption sites, simulate their photoemission spectra as a key fingerprint and compare with experiments on MgO(100) films on Ag(100). While we find only weak interaction between the cobalt centre and terrace sites on the MgO(100) surface, a strong interaction manifests itself with the low-coordinated sites. This leads to distinct features in both the valence and core-level regions of the electronic structure, as observed in the ultraviolet and X-ray photoemission spectra, corroborated by simulated spectra and calculated cobalt core-level shifts. Our work thus demonstrates the relevance of morphology-related low-coordinated sites and their properties in the adsorption of CoTPP on the MgO(100) surface.
CRIS-Team Scopus Importer:2021-02-12

Morphology of spatial patterns - Porous media, spinodal decomposition and dissipative structures - Mecke, Klaus (ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS, 1997)
The morphological characterization of patterns is becoming more and more important in Statistical Physics as complex spatial structures now emerge in many systems. A suitable family of morphological measures, known in integral geometry as Minkowski functionals, characterize not only the connectivity but also the content and shape of spatial figures. The Minkowski functionals are related to familiar geometric measures: covered volume. surface area? integral mean curvature, and Euler characteristic. Integral geometry provides powerful theorems and formulae which makes the calculus convenient for many models of stochastic geometries, e.g. for the Boolean grain model. The measures are: in particular, applicable to random patterns which consist of non-regular, fluctuating domains of homogeneous phases on a mesoscopic scale. Therefore, we illustrate the integral geometric approach by applying the morphological measures to such diverse topics as porous media, chemical-reaction patterns, and spinodal decomposition kinetics: (A) The percolation threshold of porous media can be estimated accurately in terms of the morphology of the distributed pores. (B) Turing patterns observed in chemical reaction-diffusion systems can be analyzed in tel ms of morphological measures, which turn out to be cubic polynomials in the grey-level. We observe a symmetry-breaking of the polynomials when the type of pattern changes. Therefore, the morphological measures are useful order parameters to describe pattern transitions quantitatively. (C) The time evolution of the morphology of homogeneous phases during spinodal decomposition is described, focusing: on the scaling: behavior of the morphology, Integral geometry provides a means to define the characteristic length scales and to define the cross over from the early stage decomposition to the late stage domain growth.

Morphology of spinodal decomposition - Mecke, Klaus; et al. (Physical Review E, 1997)
The morphology of homogeneous phases during spinodal decomposition, i.e., the scaling of the content, shape, and connectivity of spatial structures is described by a family of morphological measures, known as Minkowski functionals. Besides providing means to determine the characteristic length scale L in a statistically robust and computationally inexpensive way, the measures allow also one to define the crossover from the early stage decomposition to the late stage domain growth. We observe the scaling behavior L similar to t(alpha) with alpha = 1/3, alpha = 1/2, and alpha = 2/3 depending on the viscosity. When approaching the spinodal rho(sp), we recover the prediction L similar to(rho-rho(sp))(-1/2) for the early time decomposition.

Morphometric analysis in gamma-ray astronomy using Minkowski functionals Source detection via structure quantification - Göring, Daniel; Klatt, Michael; Stegmann, C.; Mecke, Klaus (Astronomy & Astrophysics, 2013)
Results. We have successfully applied our method to data of the H.E.S.S. experiment. The morphometric analysis presented here is dedicated to detecting faint extended sources.
Keywords: methods: data analysis; methods: statistical; techniques: image processing; gamma rays: diffuse background

Motion by stopping: Rectifying Brownian motion of nonspherical particles - Sporer, Susan; Goll, Christian; Mecke, Klaus (Physical Review E, 2008)
We show that Brownian motion is spatially not symmetric for mesoscopic particles embedded in a fluid if the particle is not in thermal equilibrium and its shape is not spherical. In view of applications to molecular motors in biological cells, we sustain nonequilibrium by stopping a nonspherical particle at periodic sites along a filament. Molecular dynamics simulations in a Lennard-Jones fluid demonstrate that directed motion is possible without a ratchet potential or temperature gradients if the asymmetric nonequilibrium relaxation process is hindered by external stopping. Analytical calculations in the ideal gas limit show that motion even against a fluid drift is possible and that the direction of motion can be controlled by the shape of the particle, which is completely characterized by tensorial Minkowski functionals.