Critical behavior of quantum magnets with long-range interactions in the thermodynamic limit - Fey, Sebastian; Schmidt, Kai Phillip (Physical Review B, 2016)
Quasiparticle properties of quantum magnets with long-range interactions are investigated by high-order linked-cluster expansions in the thermodynamic limit. It is established that perturbative continuous unitary transformations on white graphs are a promising and flexible approach to treat long-range interactions in quantum many-body systems. We exemplify this scheme for the one-dimensional transverse-field Ising chain with long-range interactions. For this model, the elementary quasiparticle gap is determined allowing to access the quantum-critical regime including critical exponents and multiplicative logarithmic corrections for the ferroand antiferromagnetic case.

Critical pore radius and transport properties of disordered hard- And overlapping-sphere models - Klatt, Michael; Ziff, Robert M.; Torquato, Salvatore (Physical Review E, 2021)
Transport properties of porous media are intimately linked to their pore-space microstructures. We quantify geometrical and topological descriptors of the pore space of certain disordered and ordered distributions of spheres, including pore-size functions and the critical pore radius . We focus on models of porous media derived from maximally random jammed sphere packings, overlapping spheres, equilibrium hard spheres, quantizer sphere packings, and crystalline sphere packings. For precise estimates of the percolation thresholds, we use a strict relation of the void percolation around sphere configurations to weighted bond percolation on the corresponding Voronoi networks. We use the Newman-Ziff algorithm to determine the percolation threshold using universal properties of the cluster size distribution. The critical pore radius is often used as the key characteristic length scale that determines the fluid permeability . A recent study suggested for porous media with a well-connected pore space an alternative estimate of based on the second moment of the pore size , which is easier to determine than . Here, we compare to the second moment of the pore size , and indeed confirm that, for all porosities and all models considered, is to a good approximation proportional to . However, unlike , the permeability estimate based on does not predict the correct ranking of for our models. Thus, we confirm to be a promising candidate for convenient and reliable estimates of the fluid permeability for porous media with a well-connected pore space. Moreover, we compare the fluid permeability of our models with varying degrees of order, as measured by the order metric. We find that (effectively) hyperuniform models tend to have lower values of than their nonhyperuniform counterparts. Our findings could facilitate the design of porous media with desirable transport properties via targeted pore statistics.
CRIS-Team Scopus Importer:2021-07-30

Crowding of receptors induces ring-like adhesions in model membranes - Schmidt, Daniel; Bihr, Timo; Fenz, Susanne; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Biochimica Et Biophysica Acta-Molecular Cell Research, 2015)
The dynamics of formation of macromolecular structures in adherent membranes is a key to a number of cellular processes. However, the interplay between protein reaction kinetics, diffusion and the morphology of the growing domains, governed by membrane mediated interactions, is still poorly understood. Here we show, experimentally and in simulations, that a rich phase diagram emerges from the competition between binding, cooperativity, molecular crowding and membrane spreading. In the cellular context, the spontaneously-occurring organization of adhesion domains in ring-like morphologies is particularly interesting. These are stabilized by the crowding of bulky proteins, and the membrane-transmitted correlations between bonds. Depending on the density of the receptors, this phase may be circumvented, and instead, the adhesions may grow homogeneously in the contact zone between two membranes. If the development of adhesion occurs simultaneously with membrane spreading, much higher accumulation of binders can be achieved depending on the velocity of spreading. The mechanisms identified here, in the context of our mimetic model, may shed light on the structuring of adhesions in the contact zones between two living cells. This article is part of a Special Issue entitled: Mechanobiology. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Cell adhesion; Immunological synapse; Adhesion dynamics; Membrane transmitted correlations; Ligand-receptor bonds; Crowding effects; Membrane fluctuations; Diffusion-reaction systems

Crystallization induced by multiple seeds: Dynamical density functional approach - Neuhaus, Tim; Schmiedeberg, Michael; Löwen, Hartmut (Physical Review E, 2013)
Using microscopic dynamical density functional theory, we calculate the dynamical formation of polycrystals by following the crystal growth around multiple crystalline seeds imposed to an undercooled fluid. Depending on the undercooling and the size ratio as well as the relative crystal orientation of two neighboring seeds, three possibilities of the final state emerge, namely no crystallization at all, formation of a monocrystal, or two crystallites separated by a curved grain boundary. Our results, which are obtained for two-dimensional hard disk systems using a fundamental-measure density functional, shed new light on the particle-resolved structure and growth of polycrystalline material in general.

Cu carbonyls enhance the performance of Ru-based SILP water-gas shift catalysts: a combined in situ DRIFTS and DFT study - Blaumeiser, Dominik; Stepic, Robert; Wolf, Patrick; Wick, Christian; Haumann, Marco; Wasserscheid, Peter; Smith, David M.; Smith, Ana-Suncana; Bauer, Tanja; Libuda, Jörg (Catalysis: Science and Technology, 2020)
Ru-based supported ionic liquid phase (SILP) catalysts efficiently promote the water-gas shift reaction (WGSR). The addition of CuCl further improves the performance. This is attributed to the formation of labile Cu carbonyl species, which act as CO shuttles in the ionic liquid (IL) phase. We apply in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor the formation of these Cu carbonyls in an imidazolium-based SILP system. To aid the identification of the relevant Cu carbonyls, we perform density functional theory (DFT) calculations. In the present study, we investigate [Ru(CO)(3)Cl-2](2)/CuCl/[C(4)C(1)C(1)Im]Cl/Al2O3 and CuCl/[C(4)C(1)C(1)Im]Cl/Al2O3 with various CuCl : IL ratios. The relevant Cu carbonyls are identified as neutral CuCl monomers and dimers, as well as monoanionic monomers and dimers. Moreover, we demonstrate that the ratio of the individual Cu carbonyl species depends on the CuCl : IL ratio.
CRIS-Team WoS Importer:2020-01-17

Current noise in single-molecule junctions induced by electronic-vibrational coupling - Schinabeck, Christian; Härtle, Rainer; Weber, Heiko B.; Thoss, Michael (Physical Review B, 2014)
The influence of multiple vibrational modes on current fluctuations in electron transport through single molecule junctions is investigated. Our analysis is based on a generic model of a molecular junction, which comprises a single electronic state on the molecular bridge coupled to multiple vibrational modes and fermionic leads, and employs a master equation approach. The results reveal that in molecular junctions with multiple vibrational modes, already weak to moderate electronic-vibrational coupling may result in high noise levels, especially at the onset of resonant transport, in accordance with the experimental findings of Secker et al. [Phys. Rev. Lett. 106, 136807 (2011)]. The underlying mechanisms are analyzed in some detail.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.curren

Curvature expansion of density profiles - Mecke, Klaus; et al. (EPL - Europhysics Letters, 2005)
We present a technique to calculate density profiles of a fluid close to a hard convex wall by arguing that its equilibrium density distribution depends only on the local curvatures of the wall. We perform a systematic expansion of the pro. le in powers of the curvatures and apply it to a hard-sphere fluid within the framework of density-functional theory (DFT). For large distances from the wall, the curvature expansion can be done analytically. Our approach can be generalized to systems with short-ranged fluid-fluid and wall-fluid interaction potentials, as long as intrinsic length scales remain small.

Deactivation of nitrogen donors in silicon carbide - Schmid, Frank; Pensl, Gerhard; Bockstedte, Michel Georg; Mattausch, Alexander; Pankratov, Oleg; Ohshima, T.; Itoh, H.; Weber, Heiko B.; Reshanov, Sergey (Physical Review B, 2006)
Hexagonal SiC is either co-implanted with silicon (Si+), carbon (C+), or neon (Ne+) ions along with nitrogen (N+) ions or irradiated with electrons (e-) of 200 keV energy. During the subsequent annealing step at temperatures above 1450°C a deactivation of N donors and a reduction of the compensation are observed in the case of the Si+/N+ co-implantation and e- irradiation. The N donor deactivation is investigated as a function of the concentration of the co-implanted species and the annealing temperature. The formation of energetically deep defects is analyzed with deep level transient spectroscopy. A detailed theoretical analysis based on the density functional theory is conducted; it takes into account the kinetic mechanisms for the formation of N interstitial clusters and (N-vacancy) complexes. In accordance with all the experimental results, this analysis distinctly indicates that the (NC) 4 - VSi complex, which is thermally stable at high temperatures and which has no level in the band gap of 4H-SiC, is responsible for the N donor deactivation. © 2006 The American Physical Society.
UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.IAP.LAP.deacti

Deep Learning of Quantum Many-Body Dynamics via Random Driving - Mohseni, Naeimeh; Fösel, Thomas; Guo, Lingzhen; Navarrete-Benlloch, Carlos; Marquardt, Florian (Quantum, 2022)
Neural networks have emerged as a powerful way to approach many practical problems in quantum physics. In this work, we illustrate the power of deep learning to predict the dynamics of a quantum many-body system, where the training is based purely on monitoring expectation values of observables under random driving. The trained recurrent network is able to produce accurate predictions for driving trajectories entirely different than those observed during training. As a proof of principle, here we train the network on numerical data generated from spin models, showing that it can learn the dynamics of observables of interest without needing information about the full quantum state. This allows our approach to be applied eventually to actual experimental data generated from a quantum many-body system that might be open, noisy, or disordered, without any need for a detailed understanding of the system. This scheme provides considerable speedup for rapid explorations and pulse optimization. Remarkably, we show the network is able to extrapolate the dynamics to times longer than those it has been trained on, as well as to the infinite-system-size limit.
CRIS-Team WoS Importer:2022-06-24

Deep-Sea Bioluminescence Blooms after Dense Water Formation at the Ocean Surface - Tamburini, Christian; Canals, Miquel; Houpert, Loic; Lefevre, Dominique; Martini, Verine; D'Ortenzio, Fabrizio; Robert, Anne; Testor, Pierre; Aguilar, Juan Antonio; Al Samarai, Imen; Albert, Arnaud; Andre, Michel; et al. (PLoS ONE, 2013)
The deep ocean is the largest and least known ecosystem on Earth. It hosts numerous pelagic organisms, most of which are able to emit light. Here we present a unique data set consisting of a 2.5-year long record of light emission by deep-sea pelagic organisms, measured from December 2007 to June 2010 at the ANTARES underwater neutrino telescope in the deep NW Mediterranean Sea, jointly with synchronous hydrological records. This is the longest continuous time-series of deep-sea bioluminescence ever recorded. Our record reveals several weeks long, seasonal bioluminescence blooms with light intensity up to two orders of magnitude higher than background values, which correlate to changes in the properties of deep waters. Such changes are triggered by the winter cooling and evaporation experienced by the upper ocean layer in the Gulf of Lion that leads to the formation and subsequent sinking of dense water through a process known as "open-sea convection". It episodically renews the deep water of the study area and conveys fresh organic matter that fuels the deep ecosystems. Luminous bacteria most likely are the main contributors to the observed deep-sea bioluminescence blooms. Our observations demonstrate a consistent and rapid connection between deep open-sea convection and bathypelagic biological activity, as expressed by bioluminescence. In a setting where dense water formation events are likely to decline under global warming scenarios enhancing ocean stratification, in situ observatories become essential as environmental sentinels for the monitoring and understanding of deep-sea ecosystem shifts.

Defects as a model of spacetime foam - Spinor and vector structures on the defect - Sahlmann, Hanno; Beier, Udo (2015)

Deformation of Platonic foam cells: Effect on growth rate - Evans, Myfanwy; Zirkelbach, Johannes; Schröder-Turk, Gerd; Kraynik, Andrew M.; Mecke, Klaus (Physical Review E, 2012)
The diffusive growth rate of a polyhedral cell in dry three-dimensional foams depends on details of shape beyond cell topology, in contrast to the situation in two dimensions, where, by von Neumann's law, the growth rate depends only on the number of cell edges. We analyze the dependence of the instantaneous growth rate on the shape of single foam cells surrounded by uniform pressure; this is accomplished by supporting the cell with films connected to a wire frame and inducing cell distortions by deforming the wire frame. We consider three foam cells with a very simple topology; these are the Platonic foam cells, which satisfy Plateau's laws and are based on the trivalent Platonic solids (tetrahedron, cube, and dodecahedron). The Surface Evolver is used to model cell deformations induced through extension, compression, shear, and torsion of the wire frames. The growth rate depends on the deformation mode and frame size and can increase or decrease with increasing cell distortion. The cells have negative growth rates, in general, but dodecahedral cells subjected to torsion in small wire frames can have positive growth rates. The deformation of cubic cells is demonstrated experimentally.

Demixing of homogeneous binary lipid membranes induced by protein inclusions - Nowakowski, Piotr; Stumpf, Bernd Henning; Smith, Ana-Suncana; Maciołek, Anna (Physical Review E, 2023)
We study a model of a lipid bilayer membrane described by two order parameters: the chemical composition described using the Gaussian model and the spatial configuration described with the elastic deformation model of a membrane with a finite thickness or, equivalently, for an adherent membrane. We assume and explain on physical grounds the linear coupling between the two order parameters. Using the exact solution, we calculate the correlation functions and order parameter profiles. We also study the domains that form around inclusions on the membrane. We propose and compare six distinct ways to quantify the size of such domains. Despite its simplicity, the model has many interesting features like the Fisher-Widom line and two distinct critical regions.
CRIS-Team Scopus Importer:2023-06-30

Densest Local Structures of Uniaxial Ellipsoids - Schaller, Fabian; Weigel, Robert; Kapfer, Sebastian (Physical Review X, 2016)
Connecting the collective behavior of disordered systems with local structure on the particle scale is an important challenge, for example, in granular and glassy systems. Compounding complexity, in many scientific and industrial applications, particles are polydisperse, aspherical, or even of varying shape. Here, we investigate a generalization of the classical kissing problem in order to understand the local building blocks of packings of aspherical grains. We numerically determine the densest local structures of uniaxial ellipsoids by minimizing the Set Voronoi cell volume around a given particle. Depending on the particle aspect ratio, different local structures are observed and classified by symmetry and Voronoi coordination number. In extended disordered packings of frictionless particles, knowledge of the densest structures allows us to rescale the Voronoi volume distributions onto the single-parameter family of k-Gamma distributions. Moreover, we find that approximate icosahedral clusters are found in random packings, while the optimal local structures for more aspherical particles are not formed.
EAM Import::2019-03-13

Density functional theory of heterogeneous crystallization - Neuhaus, Tim; Härtel, Andreas; Marechal, Mattheus; Schmiedeberg, Michael; Löwen, Hartmut (European Physical Journal - Special Topics, 2014)
This mini-review summarizes recent progress in describing heterogeneous crystallization processes and microstructure formation within microscopic classical density functional theory (DFT). After outlining the basic features of DFT, we discuss several applications ranging from the structure and thermodynamics of fluid-crystal interfaces for hard sphere and Yukawa systems to dynamical phenomena such as crystal growth on structured substrates and induced by externally imposed seeds.

Deriving fundamental measure theory from the virial series: Consistency with the zero-dimensional limit - Marechal, Mattheus; Korden, Stephan; Mecke, Klaus (Physical Review E, 2014)
Fundamental measure theory (FMT) for hard particles has great potential for predicting the phase behavior of colloidal and nanometric shapes. The modern versions of FMT are usually derived from the zero-dimensional limit, a system of at most one particle confined in a collection of cavities in the limit that all cavities shrink to the size of the particle. In Phys. Rev. E 85, 041150 (2012), a derivation from an approximated and resummed virial expansion was presented, whose result was not fully consistent with the FMT from the zero-dimensional limit. Here we improve on this derivation and obtain exactly the same FMT functional as was obtained earlier from the zero-dimensional limit. As a result, further improvements of FMT based on the virial expansion can now be formulated, some of which we suggest in the outlook.

Description of collective nuclear dynamics by density functional theory with Skyrme forces - Nesterenko, V. O.; Kleinig, W.; Kvasil, J.; Vesely, P.; Reinhard, Paul-Gerhard; Novikov, A. S. (2nd International Conference on Current Problems in Nuclear Physics and Atomic Energy, NPAE 2008 - Proceedings, 2009)
Ability of the time-dependent density functional theory (TDDFT) with Skyrme forces to describe electric giant resonances (GR) is scrutinized within the self-consistent separable RPA (SRPA) method recently developed by our group. The isovector E1(T = 1) and isoscalar E2(T = 0) and E0(T = 0) GR are explored with different Skyrme forces. Both spherical and deformed nuclei in rare-earth, actinide and superheavy regions are considered. A special attention is paid to the role of time-odd densities in the Skyrme functional, which are known to restore Galilean invariance violated by velocity-dependent time-even densities. The tentative classification of Skyrme forces, based on the description of isovector GR with time-odd densities, is proposed. It is shown that inclusion of these densities leads to much closer results of different Skyrme forces for the E0(T = 0) and so for compressibility of finite nuclei. The systematic SRPA calculations with the force SLy6 demonstrate nice agreement with available experimental data for the isovector E1(T = 1) in rare-earth and actinide nuclei and high predictability of the model for superheavy elements. The structure of E1(T = 1) right flank is discussed and its enhanced vorticity is predicted.
CRIS-Team Scopus Importer:2023-07-24

Design of an optomagnonic crystal: Towards optimal magnon-photon mode matching at the microscale - Graf, Jasmin; Sharma, Sanchar; Huebl, Hans; Viola Kusminskiy, Silvia (Physical Review Research, 2021)
We put forward the concept of an optomagnonic crystal: a periodically patterned structure at the microscale based on a magnetic dielectric, which can co-localize magnon and photon modes. The co-localization in small volumes can result in large values of the photon-magnon coupling at the single quanta level, which opens perspectives for quantum information processing and quantum conversion schemes with these systems. We study theoretically a simple geometry consisting of a one-dimensional array of holes with an abrupt defect, considering the ferrimagnet yttrium iron garnet (YIG) as the basis material. We show that both magnon and photon modes can be localized at the defect, and use symmetry arguments to select an optimal pair of modes in order to maximize the coupling. We show that an optomagnonic coupling in the kHz range is achievable in this geometry, and discuss possible optimization routes in order to improve both coupling strengths and optical losses.
CRIS-Team Scopus Importer:2021-10-08

Detecting structured sources in noisy images via Minkowski maps - Klatt, Michael A.; Mecke, Klaus (EPL - Europhysics Letters, 2019)
Astronomy, biophysics, and material science often depend on the possibility to extract information out of faint spatial signals. Here we present a morphometric analysis technique to quantify the shape of structural deviations in greyscale images. It identifies important features in noisy spatial data, especially for short observation times and low statistics. Without assuming any prior knowledge about potential sources, the additional shape information can increase the sensitivity by 14 orders of magnitude compared to previous methods. Rejection rates can increase by an order of magnitude. As a key ingredient to such a dramatic increase, we accurately describe the distribution of the homogeneous background noise in terms of the density of states Omega(A, P, chi) for the area A, perimeter P, and Euler characteristic. of random black-and-white images. The technique is successfully applied to data of the H.E.S.S. experiment for the detection of faint extended sources. Copyright (C) EPLA, 2020
CRIS-Team WoS Importer:2020-05-08

Detection of phonon and phason modes in intrinsic colloidal quasicrystals by reconstructing their structure in hyperspace - Hielscher, Johannes; Martinsons, Miriam; Schmiedeberg, Michael; Kapfer, Sebastian (Journal of Physics: Condensed Matter, 2017)
Phasons are additional degrees of freedom which occur in quasicrystals alongside the phonons known from conventional periodic crystals. The rearrangements of particles that are associated with a phason mode are hard to interpret in physical space. We reconstruct the quasicrystal structure by an embedding into extended higher-dimensional space, where phasons correspond to displacements perpendicular to the physical space. In dislocation-free decagonal colloidal quasicrystals annealed with Brownian dynamics simulations, we identify thermal phonon and phason modes. Finite phononic strain is pinned by phasonic excitations even after cooling down to zero temperature. For the phasonic displacements underlying the flip pattern, the reconstruction method gives an approximation within the limits of a multi-mode harmonic ansatz, and points to fundamental limitations of a harmonic picture for phasonic excitations in intrinsic colloidal quasicrystals.
Keywords: colloids; quasicrystals; phasons; phonons

Detection potential of the KM3NeT detector for high-energy neutrinos from the Fermi bubbles - Adrian-Martinez, S.; Ageron, M.; Aguilar, J. A.; Aharonian, F.; Aiello, S.; Albert, A.; Alexandri, M.; Ameli, F.; Anassontzis, E. G.; Anghinolfi, M.; Anton, Gisela; Anvar, S.; et al. (Astroparticle Physics, 2013)
A recent analysis of the Fermi Large Area Telescope data provided evidence for a high-intensity emission of high-energy gamma rays with a E-2 spectrum from two large areas, spanning 50 above and below the Galactic centre (the "Fermi bubbles"). A hadronic mechanism was proposed for this gamma-ray emission making the Fermi bubbles promising source candidates of high-energy neutrino emission. In this work Monte Carlo simulations regarding the detectability of high-energy neutrinos from the Fermi bubbles with the future multi-km(3) neutrino telescope KM3NeT in the Mediterranean Sea are presented. Under the hypothesis that the gamma-ray emission is completely due to hadronic processes, the results indicate that neutrinos from the bubbles could be discovered in about one year of operation, for a neutrino spectrum with a cutoff at 100 TeV and a detector with about 6 km(3) of instrumented volume. The effect of a possible lower cutoff is also considered. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Neutrino telescope; Fermi Bubbles; KM3NeT

Dialogisches Denken. Ein Plädoyer für die Etablierung einer Kultur des wechselseitigen Austausches von Denk-Positionen zwischen Physikern, Dichtern und Literaturwissenschaftlern - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Dichotomy between Large Local and Small Ordered Magnetic Moments in Iron-Based Superconductors - Hansmann, Philipp; Arita, Ryotaro; Toschi, Alessandro; Sakai, S.; Sangiovanni, Giorgio; Held, Karsten (Physical Review Letters, 2010)
We study a four-band model for iron-based superconductors within the local density approximation combined with dynamical mean-field theory (LDA + DMFT). This successfully reproduces the results of models which take As p degrees of freedom explicitly into account and has several physical advantages over the standard five d-band model. Our findings reveal that the new superconductors are more strongly correlated than their single-particle properties suggest. Two-particle correlation functions unveil the dichotomy between local and ordered magnetic moments in these systems, calling for further experiments to better resolve the short time scale spin dynamics.
CRIS-Team WoS Importer:2020-02-19

Die Formel als Gedicht [Interview von Marie-Luise Goldmann] - Mecke, Klaus; Heydenreich, Aura (2018)
Prof. Dr. Klaus Mecke ist theoretischer Physiker, Dr. Aura Heydenreich Germanistin. Gemeinsam forschen sie am Erlanger Zentrum für Literatur und Naturwissenschaft (ELINAS), einem interdisziplinären Forum, das sich dem wechselseitigen Wissenstransfer zwischen Physik und Literatur widmet. Ein Gespräch über die Bedeutung der Metapher für die Physik, das poetologisczhe Potential naturwissenschaftlicher Forschung und das Klischee des einsamen Genies.<br

Die Zeit ist der Abgrund, in den wir fallen.Thomas Lehr im Dialog zu »42« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Diffeomorphism-invariant quantum field theories of connections in terms of webs - Lewandowski, Jerzy; Thiemann, Thomas (Classical and Quantum Gravity, 1999)
In the canonical quantization of gravity in terms of the Ashtekar variables one uses paths in the 3-space to construct the quantum states. Usually, one restricts oneself to families of paths admitting only a finite number of isolated intersections. This assumption implies a limitation on the diffeomorphisms invariance of the introduced structures. In this work, using the previous results of Baez and Sawin, we extend the existing results to a theory admitting all the possible piecewise-smooth finite paths and loops. In particular, we (a) characterize the spectrum of the Ashtekar-Isham configuration space, (b) introduce spin-web states, a generalization of the spin network states, (c) extend the diffeomorphism averaging to the spin-web states and derive a large class of diffeomorphism-invariant states and finally (d) extend the 3-geometry operators and the Hamiltonian operator.

Differential Source Count for Gamma-Ray Bursts - Banerjee, Shreya; Eichler, David; Guetta, Dafne (Astrophysical Journal, 2021)
Different forms of long gamma-ray burst (GRB) luminosity functions are considered on the basis of an explicit physical model. The inferred flux distributions are compared with the observed ones from two samples of GRBs, Swift and Fermi GBM. The best-fit parameters of the luminosity functions are found, and the physical interpretations are discussed. The results are consistent with the observation of a comparable number of flat-phase afterglows and monotonically decreasing ones.
CRIS-Team WoS Importer:2021-11-12

Dirac-Observablen in der Kosmolgie - Zöbelein, Carolin; Giesel, Kristina (2013)

Directed percolation identified as equilibrium pre-transition towards non-equilibrium arrested gel states - Kohl, M.; Capellmann, R. F.; Laurati, Marco; Egelhaaf, S. U.; Schmiedeberg, Michael (Nature Communications, 2016)
The macroscopic properties of gels arise from their slow dynamics and load-bearing network structure, which are exploited by nature and in numerous industrial products. However, a link between these structural and dynamical properties has remained elusive. Here we present confocal microscopy experiments and simulations of gel-forming colloid-polymer mixtures. They reveal that gel formation is preceded by continuous and directed percolation. Both transitions lead to system-spanning networks, but only directed percolation results in extremely slow dynamics, ageing and a shrinking of the gel that resembles synaeresis. Therefore, dynamical arrest in gels is found to be linked to a structural transition, namely directed percolation, which is quantitatively associated with the mean number of bonded neighbours. Directed percolation denotes a universality class of transitions. Our study hence connects gel formation to a well-developed theoretical framework, which now can be exploited to achieve a detailed understanding of arrested gels.

Direct implementation of a perceptron in superconducting circuit quantum hardware - Pechal, Marek; Roy, Federico; Wilkinson, Samuel; Salis, Gian; Werninghaus, Max; Hartmann, Michael; Filipp, Stefan (Physical Review Research, 2022)
The utility of classical neural networks as universal approximators suggests that their quantum analogues could play an important role in quantum generalizations of machine-learning methods. Inspired by the proposal in Torrontegui and Garcia-Ripoll [Europhys. Lett. 125, 30004 (2019)], we demonstrate a superconducting qubit implementation of a controlled gate, which generalizes the action of a classical perceptron as the basic building block of a quantum neural network. In a two-qubit setup we show full control over the steepness of the perceptron activation function, the input weight and the bias by tuning the gate length, the coupling between the qubits, and the frequency of the applied drive, respectively. In its general form, the gate realizes a multiqubit entangling operation in a single step, whose decomposition into single-and two-qubit gates would require a number of gates that is exponential in the number of qubits. Its demonstrated direct implementation as perceptron in quantum hardware may therefore lead to more powerful quantum neural networks when combined with suitable additional standard gates.
CRIS-Team WoS Importer:2022-09-23

Direct relations between morphology and transport in Boolean models - Scholz, Christian; Klatt, Michael; Mecke, Klaus; Wirner, Frank; Hirneise, Daniel; Schröder-Turk, Gerd; Bechinger, Clemens (Physical Review E, 2015)
We study the relation of permeability and morphology for porous structures composed of randomly placed overlapping circular or elliptical grains, so-called Boolean models. Microfluidic experiments and lattice Boltzmann simulations allowus to evaluate a power-lawrelation between theEuler characteristic of the conducting phase and its permeability. Moreover, this relation is so far only directly applicable to structures composed of overlapping grains where the grain density is known a priori. We develop a generalization to arbitrary structures modeled by Boolean models and characterized by Minkowski functionals. This generalization works well for the permeability of the void phase in systems with overlapping grains, but systematic deviations are found if the grain phase is transporting the fluid. In the latter case our analysis reveals a significant dependence on the spatial discretization of the porous structure, in particular the occurrence of single isolated pixels. To link the results to percolation theory we performed Monte Carlo simulations of the Euler characteristic of the open cluster, which reveals different regimes of applicability for our permeability-morphology relations close to and far away from the percolation threshold.

Dislocation and node states in bilayer graphene systems - Weckbecker, Dominik; Gupta, Reena; Rost, Fabian; Sharma, S.; Shallcross, Sam (Physical Review B, 2019)
We investigate the electronic structure of realistic partial dislocation networks in bilayer graphene that feature annihilating, wandering, and intersecting partial lines. We find charge accumulation states at partials that are sensitive to Fermi energy and partial Burgers vector but not to the screw versus edge character of the partial. These states are shown to be current carrying, with the current density executing a spiral motion along the dislocation line with a strong interlayer component to the current. Close to the Dirac point, localization on partials switches to localization on intersections of partials, with a corresponding complex current flow around the nodes.
CRIS-Team WoS Importer:2021-10-18

Dislocation-free growth of quasicrystals from two seeds due to additional phasonic degrees of freedom - Schmiedeberg, Michael; Achim, Cristian; Hielscher, Johannes; Kapfer, Sebastian; Loewen, Hartmut (Physical Review E, 2017)
We explore the growth of two-dimensional quasicrystals, i.e., aperiodic structures that possess long-range order, from two seeds at various distances and with different orientations by using dynamical phase-field crystal calculations. We compare the results to the growth of periodic crystals from two seeds. There, a domain border consisting of dislocations is observed in case of large distances between the seed and large angles between their orientation. Furthermore, a domain border is found if the seeds are placed at a distance that does not fit to the periodic lattice. In the case of the growth of quasicrystals, we only observe domain borders for large distances and different orientations. Note that all distances do inherently not match to a perfect domain wall-free quasicrystalline structure. Nevertheless, we find dislocation-free growth for all seeds at a small enough distance and for all seeds that approximately have the same orientation. In periodic structures, the stress that occurs due to incommensurate distances between the seeds results in phononic strain fields or, in the case of too large stresses, in dislocations. In contrast, in quasicrystals an additional phasonic strain field can occur and suppress dislocations. Phasons are additional degrees of freedom that are unique to quasicrystals. As a consequence, the additional phasonic strain field helps to distribute the stress and facilitates the growth of dislocation-free quasicrystals from multiple seeds. In contrast, in the periodic case the growth from multiple seeds most likely leads to a structure with multiple domains. Our work lays the theoretical foundations for growing perfect quasicrystals from different seeds and is therefore relevant for many applications.

Disorder by disorder and flat bands in the kagome transverse field Ising model - Powalski, M.; Coester, K.; Moessner, R.; Schmidt, Kai Phillip (Physical Review B, 2013)
We study the transverse field Ising model on a kagome and a triangular lattice using high-order series expansions about the high-field limit. For the triangular lattice our results confirm a second-order quantum phase transition in the 3d XY universality class. Our findings for the kagome lattice indicate a notable instance of a disorder by disorder scenario in two dimensions. The latter follows from a combined analysis of the elementary gap in the high- and low-field limit which is shown to stay finite for all fields h. Furthermore, the lowest one-particle dispersion for the kagome lattice is extremely flat acquiring a dispersion only from order 8 in the 1/h limit. This behavior can be traced back to the existence of local modes and their breakdown which is understood intuitively via the linked cluster expansion. DOI: 10.1103/PhysRevB.87.054404

Disordered spherical bead packs are anisotropic - Schröder-Turk, Gerd; Mickel, Walter; Schröter, Matthias; Delaney, Gary; Saadatfar, Mohammad; Senden, T.J.; Mecke, Klaus; Aste, T. (EPL - Europhysics Letters, 2010)
Investigating how tightly objects pack space is a long-standing problem, with relevance for many disciplines from discrete mathematics to the theory of glasses. Here we report on the fundamental yet so far overlooked geometric property that disordered mono-disperse spherical bead packs have significant local structural anisotropy manifest in the shape of the free space associated with each bead. Jammed disordered packings from several types of experiments and simulations reveal very similar values of the cell anisotropy, showing a linear decrease with packing fraction. Strong deviations from this trend are observed for unjammed configurations and for partially crystalline packings above 64%. These findings suggest an inherent geometrical reason why, in disordered packings, anisotropic shapes can fill space more efficiently than spheres, and have implications for packing effects in non-spherical liquid crystals, foams and structural glasses.

Dissipation and energy balance in electronic dynamics of Na clusters - Vincendon, Marc; Suraud, Eric; Reinhard, Paul Gerhard (European Physical Journal D, 2017)
Abstract: We investigate the impact of dissipation on the energy balance in the electron dynamics of metal clusters excited by strong electro-magnetic pulses. The dynamics is described theoretically by Time-Dependent Density-Functional Theory (TDDFT) at the level of Local Density Approximation (LDA) augmented by a self interaction correction term and a quantum collision term in Relaxation-Time Approximation (RTA). We evaluate the separate contributions to the total excitation energy, namely energy exported by electron emission, potential energy due to changing charge state, intrinsic kinetic and potential energy, and collective flow energy. The balance of these energies is studied as function of the laser parameters (frequency, intensity, pulse length) and as function of system size and charge. We also look at collisions with a highly charged ion and here at the dependence on the impact parameter (close versus distant collisions). Dissipation turns out to be small where direct electron emission prevails namely for laser frequencies above any ionization threshold and for slow electron extraction in distant collisions. Dissipation is large for fast collisions and at low laser frequencies, particularly at resonances. Graphical abstract: [Figure not available: see fulltext.].
CRIS-Team Scopus Importer:2023-07-24

Distinct spin and orbital dynamics in Sr2RuO4 - Suzuki, H.; Wang, L.; Bertinshaw, J.; Strand, H. U.R.; Käser, Stefan; Krautloher, M.; Yang, Z.; Wentzell, N.; Parcollet, O.; Jerzembeck, F.; Kikugawa, N.; Mackenzie, A. P.; et al. (Nature Communications, 2023)
The unconventional superconductor Sr2RuO4 has long served as a benchmark for theories of correlated-electron materials. The determination of the superconducting pairing mechanism requires detailed experimental information on collective bosonic excitations as potential mediators of Cooper pairing. We have used Ru L 3-edge resonant inelastic x-ray scattering to obtain comprehensive maps of the electronic excitations of Sr2RuO4 over the entire Brillouin zone. We observe multiple branches of dispersive spin and orbital excitations associated with distinctly different energy scales. The spin and orbital dynamical response functions calculated within the dynamical mean-field theory are in excellent agreement with the experimental data. Our results highlight the Hund metal nature of Sr2RuO4 and provide key information for the understanding of its unconventional superconductivity.
CRIS-Team Scopus Importer:2023-11-17

Doubly special relativity - Lohberger, Johannes; Sahlmann, Hanno (2014)

Dressed metric predictions revisited - Kaminski, Wojciech; Kolanowski, Maciej; Lewandowski, Jerzy (Classical and Quantum Gravity, 2020)
It was recently shown that the volume operator of loop quantum cosmology (LQC) and all its positive powers are ill-defined on physical states. In this paper, we investigate how it effects predictions of cosmic microwave background (CMB) power spectra obtained within dressed metric approach for which expectations values of a are the key element. We find that almost every step in the procedure is ill-defined and relies heavily upon a (seemingly premature) numerical truncation. Thus, it suggests that more care is needed in making predictions regarding pre-inflationary physics. We propose a new scheme which contains only well-defined quantities. The surprising agreement of the hitherto models with observational data, especially at low angular momenta l is explained.
CRIS-Team WoS Importer:2020-04-17

Driven electronic bridge processes via defect states in Th 229 -doped crystals - Nickerson, Brenden S.; Pimon, Martin; Bilous, Pavlo; Gugler, Johannes; Kazakov, Georgy A.; Sikorsky, Tomas; Beeks, Kjeld; Grueneis, Andreas; Schumm, Thorsten; Pálffy, Adriana (Physical Review A, 2021)
The electronic defect states resulting from doping Th229 in CaF2 offer a unique opportunity to excite the nuclear isomeric state Th229m at approximately 8 eV via electronic bridge mechanisms. We consider bridge schemes involving stimulated emission and absorption using an optical laser. The role of different multipole contributions, both for the emitted or absorbed photon and nuclear transition, to the total bridge rates are investigated theoretically. We show that the electric dipole component is dominant for the electronic bridge photon. In contradistinction, the electric quadrupole channel of the Th229 isomeric transition plays the dominant role for the bridge processes presented. The driven bridge rates are discussed in the context of background signals in the crystal environment and of implementation methods. We show that inverse electronic bridge processes quenching the isomeric state population can improve the performance of a solid-state nuclear clock based on Th229m.
CRIS-Team Scopus Importer:2021-06-11

Duality defects in E 8 - Burbano, Ivan M.; Kulp, Justin; Neuser, Jonas (Journal of High Energy Physics, 2022)
We classify all non-invertible Kramers-Wannier duality defects in the E8 lattice Vertex Operator Algebra (i.e. the chiral (E8)1 WZW model) coming from ℤm symmetries. We illustrate how these defects are systematically obtainable as ℤ2 twists of invariant sub-VOAs, compute defect partition functions for small m, and verify our results against other techniques. Throughout, we focus on taking a physical perspective and highlight the important moving pieces involved in the calculations. Kac’s theorem for finite automorphisms of Lie algebras and contemporary results on holomorphic VOAs play a role. We also provide a perspective from the point of view of (2+1)d Topological Field Theory and provide a rigorous proof that all corresponding Tambara-Yamagami actions on holomorphic VOAs can be obtained in this manner. We include a list of directions for future studies.
CRIS-Team Scopus Importer:2022-11-18
Keywords: Anomalies in Field and String Theories; Discrete Symmetries; Global Symmetries

Dunkle Energie - Ernst, Joseph Felix; Heydenreich, Aura; Krömer, Philip; Mecke, Klaus (homunculus verlag, 2016)
Seitenstechen ist die jährlich erscheinende Literaturzeitschrift des homunculus verlags. Sie vereint Texte aktueller Autoren mit klassischen Werken aller belletristischen Gattungen zu einem wechselnden Thema, auf dass die Literatur die zeitliche Distanz überwinde und eins werde. Seitenstechen ist ein Gesamtkunstwerk voller Neu- und Wiederentdeckungen. Nach einer erfolgreichen #1 mit Beiträgen zu Meer und Seefahrt begibt sich die #2 hinaus ins All und hinein in die dunkelsten Winkel der menschlichen Seele. Das Thema lautet Dunkle Energie, die große Unbekannte, welche die Astrophysiker annehmen, um die Expansion des Universums erklären zu können. Dunkle Energie kann aber auch das Moment bezeichnen, das den Menschen antreibt, umtreibt und im Innersten zusammenhält oder zerreißt. Jeder Beitrag präsentiert seine individuelle Auslegung des Phänomens. Mitherausgegeber der zweiten Ausgabe von Seitenstechen ist ELINAS, das Erlanger Zentrum für Literatur und Naturwissenschaft. Mit Texten von Dante Alighieri, Thomas von Aquin, Aristoteles, Florian L. Arnold, Timo Brandt, Lord Byron, Manfred Chobot, Andreas Christ, Ulrike Draesner, Christopher Ecker, Albert Einstein, Tobias Falberg, Gabriele Frings, Galileo Galilei, Axel Görlach, Durs Grünbein, Caroline Hartge, Ulrich Holbein, Harald Kappel, Bastian Kienitz, Robert Kraft, Georges Lemaître, Lukrez, James Clerk Maxwell, Martin Piekar, Platon, Edgar Allan Poe, Raoul Schrott, Eli A. Solaris, Alke Stachler, Armin Steigenberger, Olaf Trunschke, Ulrich Woel

Dunkle Energie im Universum der Schrift – Zwischen Kosmologie und Poesie. Vorwort - Heydenreich, Aura; Mecke, Klaus (Dunkle Energie, 2016)

Dynamical Backaction Magnomechanics - Potts, C. A.; Varga, E.; Bittencourt, V. A. S. V.; Viola Kusminskiy, Silvia; Davis, J. P. (Physical Review X, 2021)
Dynamical backaction resulting from radiation pressure forces in optomechanical systems has proven to be a versatile tool for manipulating mechanical vibrations. Notably, dynamical backaction has resulted in the cooling of a mechanical resonator to its ground state, driving phonon lasing, the generation of entangled states, and observation of the optical-spring effect. In certain magnetic materials, mechanical vibrations can interact with magnetic excitations (magnons) via the magnetostrictive interaction, resulting in an analogous magnon-induced dynamical backaction. In this article, we directly observe the impact of magnon-induced dynamical backaction on a spherical magnetic sample's mechanical vibrations. Moreover, dynamical backaction effects play a crucial role in many recent theoretical proposals; thus, our work provides the foundation for future experimental work pursuing many of these theoretical proposals.Y
CRIS-Team WoS Importer:2021-09-24

Dynamically generated synthetic electric fields for photons - Zapletal, Petr; Walter, Stefan; Marquardt, Florian (Physical Review A, 2019)
Static synthetic magnetic fields give rise to phenomena including the Lorentz force and the quantum Hall effect even for neutral particles, and they have by now been implemented in a variety of physical systems. Moving toward fully dynamical synthetic gauge fields allows, in addition, for backaction of the particles' motion onto the field. If this results in a time-dependent vector potential, conventional electromagnetism predicts the generation of an electric field. Here, we show how synthetic electric fields for photons arise self-consistently due to the nonlinear dynamics in a driven system. Our analysis is based on optomechanical arrays, where dynamical gauge fields arise naturally from phonon-assisted photon tunneling. We study open, one-dimensional arrays, where synthetic magnetic fields are absent. However, we show that synthetic electric fields can be generated dynamically. The generation of these fields depends on the direction of photon propagation, leading to a mechanism for a photon diode, inducing nonlinear unidirectional transport via dynamical synthetic gauge fields.
CRIS-Team WoS Importer:2019-08-16

Dynamically implementing the μ-bar-scheme in cosmological and spherically symmetric models in an extended phase space model - Giesel, Kristina; Liu, Hongguang (Universe, 2023)
We consider an extended phase space formulation for cosmological and spherically symmetric models in which the choice of a given μ¯" role="presentation" style="max-height: none; display: inline; line-height: normal; font-size: 13.2px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: Arial, Arial, Helvetica, sans-serif; position: relative;">μ¯¯-scheme can be implemented dynamically. These models are constructed in the context of the relational formalism by using a canonical transformation on the extended phase space, which provides a Kuchař decomposition of the extended phase space. The resulting model can be understood as a gauge-unfixed model of a given μ¯" role="presentation" style="max-height: none; display: inline; line-height: normal; font-size: 13.2px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: Arial, Arial, Helvetica, sans-serif; position: relative;">μ¯¯-scheme. We use this formalism to investigate the restrictions to the allowed μ¯" role="presentation" style="max-height: none; display: inline; line-height: normal; font-size: 13.2px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: Arial, Arial, Helvetica, sans-serif; position: relative;">μ¯¯-scheme from this perspective and discuss the differences in the cosmological and spherically symmetric case. This method can be useful, for example, to obtain a μ¯" role="presentation" style="max-height: none; display: inline; line-height: normal; font-size: 13.2px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: Arial, Arial, Helvetica, sans-serif; position: relative;">μ¯¯-scheme in a top-down derivation from full LQG to symmetry-reduced effective models, where, for some models, only the μ0" role="presentation" style="max-height: none; display: inline; line-height: normal; font-size: 13.2px; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; caret-color: rgb(34, 34, 34); color: rgb(34, 34, 34); font-family: Arial, Arial, Helvetica, sans-serif; position: relative;">μ0-scheme has been obtained thus far.<br

Dynamically induced doublon repulsion in the Fermi-Hubbard model probed by a single-particle density of states - Valmispild, V. N.; Dutreix, C.; Eckstein, Martin; Katsnelson, M.; Lichtenstein, A.; Stepanov, E. A. (Physical Review B, 2020)
We investigate the possibility to control dynamically the interactions between repulsively bound pairs of fermions (doublons) in correlated systems with off-resonant ac fields. We introduce an effective Hamiltonian that describes the physics of doublons up to second order in the high-frequency limit. It unveils that the doublon interaction, which is attractive in equilibrium, can be completely suppressed and then switched to repulsive by varying the power of the ac field. We show that the signature of the dynamical repulsion between doublons can be found in the single-fermion density of states averaged in time. Our results are further supported by nonequilibrium dynamical mean-field theory simulations for the half-filled Fermi-Hubbard model.
CRIS-Team WoS Importer:2020-12-18

Dynamical mean-field study of a photon-mediated ferroelectric phase transition - Lenk, Katharina; Li, Jiajun; Werner, Philipp; Eckstein, Martin (Physical Review B, 2022)
The interplay of light and matter gives rise to intriguing cooperative effects in quantum many-body systems. This is even true in thermal equilibrium, where the electromagnetic field can hybridize with collective modes of matter, and virtual photons can induce interactions in the solid. Here, we show how these light-mediated interactions can be treated using the dynamical mean-field theory formalism. We consider a minimal model of a two-dimensional material that couples to a surface plasmon polariton mode of a metal-dielectric interface. Within the mean-field approximation, the system exhibits a ferroelectric phase transition that is unaffected by the light-matter coupling. Bosonic dynamical mean-field theory provides a more accurate description and reveals that the photon-mediated interactions enhance the ferroelectric order and stabilize the ferroelectric phase.
CRIS-Team WoS Importer:2023-01-13

Dynamical phase transitions in the collisionless pre-thermal states of isolated quantum systems: Theory and experiments - Marino, Jamir; Eckstein, Martin; Foster, Matthew S.; Rey, Ana Maria (Reports on Progress in Physics, 2022)
We overview the concept of dynamical phase transitions (DPTs) in isolated quantum systems quenched out of equilibrium. We focus on non-equilibrium transitions characterized by an order parameter, which features qualitatively distinct temporal behavior on the two sides of a certain dynamical critical point. DPTs are currently mostly understood as long-lived prethermal phenomena in a regime where inelastic collisions are incapable to thermalize the system. The latter enables the dynamics to substain phases that explicitly break detailed balance and therefore cannot be encompassed by traditional thermodynamics. Our presentation covers both cold atoms as well as condensed matter systems. We revisit a broad plethora of platforms exhibiting pre-thermal DPTs, which become theoretically tractable in a certain limit, such as for a large number of particles, large number of order parameter components, or large spatial dimension. The systems we explore include, among others, quantum magnets with collective interactions, φ 4 quantum field theories, and Fermi-Hubbard models. A section dedicated to experimental explorations of DPTs in condensed matter and AMO systems connects this large variety of theoretical models.
CRIS-Team Scopus Importer:2022-11-04
Keywords: collisionless pre-thermal states; dynamical phase transitions; isolated quantum systems

Dynamical Properties of the Mukhanov-Sasaki Hamiltonian - Kobler, Michael; Giesel, Kristina (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2018)
The inflationary epoch at the beginning of the universe is commonly described within the frame- work of (linear) cosmological perturbation theory. The corresponding equation of motion for the gauge-invariant perturbations is the Mukhanov-Sasaki equation, which resembles a time-dependent harmonic oscillator. At first we will consider a mechanical analogue of the Mukhanov-Sasaki equa- tion and use the known Lewis-Riesenfeld invariant and the extended phase space formalism in- troduced in previous works in order to analyse the system. These techniques allow to construct an extended canonical transformation that maps an explicitly time-dependent Hamiltonian into a time-independent one. The generators of this symplectic map can in turn be canonically quan- tised on the original part of the phase space, which is the constraint hypersurface of the extended theory, connecting to recent publications. Our further analysis leads us to a closed form of the time-evolution operator for the single-mode Mukhanov-Sasaki Hamiltonian, that is to the associ- ated Dyson series. We will analyse the characteristic properties of this time-evolution operator and discuss whether it can be extended to the full Fock space. Finally we give an outlook towards possible applications of these techniques to inflationary quantum cosmology.

Dynamical properties of the Mukhanov-Sasaki hamiltonian in the context of adiabatic vacua and the Lewis-Riesenfeld invariant - Fahn, Max Joseph; Giesel, Kristina; Kobler, Michael (Universe, 2019)
We use the method of the Lewis-Riesenfeld invariant to analyze the dynamical properties of the Mukhanov-Sasaki Hamiltonian and, following this approach, investigate whether we can obtain possible candidates for initial states in the context of inflation considering a quasi-de Sitter spacetime. Our main interest lies in the question of to which extent these already well-established methods at the classical and quantum level for finitely many degrees of freedom can be generalized to field theory. As our results show, a straightforward generalization does in general not lead to a unitary operator on Fock space that implements the corresponding time-dependent canonical transformation associated with the Lewis-Riesenfeld invariant. The action of this operator can be rewritten as a time-dependent Bogoliubov transformation, where we also compare our results to already existing ones in the literature. We show that its generalization to Fock space has to be chosen appropriately in order to not violate the Shale-Stinespring condition. Furthermore, our analysis relates the Ermakov differential equation that plays the role of an auxiliary equation, whose solution is necessary to construct the Lewis-Riesenfeld invariant, as well as the corresponding time-dependent canonical transformation, to the defining differential equation for adiabatic vacua. Therefore, a given solution of the Ermakov equation directly yields a full solution of the differential equation for adiabatic vacua involving no truncation at some adiabatic order. As a consequence, we can interpret our result obtained here as a kind of non-squeezed Bunch-Davies mode, where the term non-squeezed refers to a possible residual squeezing that can be involved in the unitary operator for certain choices of the Bogoliubov map.
CRIS-Team Scopus Importer:2019-08-16
Keywords: Adiabatic vacua; Bogoliubov transformation; Cosmological perturbation theory; Lewis-Riesenfeld invariant; Quantum cosmology

Dynamical Simulation of Electron Transfer Processes in Alkanethiolate Self-Assembled Monolayers at the Au(111) Surface - Prucker, Veronika; Rubio-Pons, Oscar; Bockstedte, Michel Georg; Wang, Haobin; Brana Coto, Pedro; Thoss, Michael (Journal of Physical Chemistry C, 2013)
Electron transfer is investigated in a series of self-assembled monolayers (SAMs) consisting of nitrile-substituted short chain alkanethiolate molecules adsorbed at the Au(111) surface. Using first-principles methods and a model electron transfer Hamiltonian, we analyze the main factors controlling, at the molecular level, the electron injection times from donor states localized at the tail group of the SAM into the Au(111) substrate. We show that the donor-acceptor electronic couplings depend significantly on the orbital symmetry of the donor state and the length of the aliphatic spacer chain of the SAM. The dependence on the donor state symmetry and on the molecular structure of the linker can be used to control the electron injection times even in situations where the energy separation between the donor states is smaller than their width. © 2013 American Chemical Society.
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.ITP.ppem.dynami

Dynamical states in driven colloidal liquid crystals - Fischermeier, Ellen; Marechal, Mattheus; Mecke, Klaus (Journal of Chemical Physics, 2014)
We study a model colloidal liquid crystal consisting of hard spherocylinders under the influence of an external aligning potential by Langevin dynamics simulation. The external field that rotates in a plane acts on the orientation of the individual particles and induces a variety of collective nonequilibrium states. We characterize these states by the time-resolved orientational distribution of the particles and explain their origin using the single particle behavior. By varying the external driving frequency and the packing fraction of the spherocylinders we construct the dynamical state diagram. (C) 2014 AIP Publishing LLC.

Dynamic decay and superadiabatic forces in the van Hove dynamics of bulk hard sphere fluids - Treffenstaedt, Lucas L.; Schindler, Thomas; Schmidt, Matthias (SciPost Physics, 2022)
We study the dynamical decay of the van Hove function of Brownian hard spheres using event-driven Brownian dynamics simulations and dynamic test particle theory. Relevant decays mechanisms include deconfinement of the self particle, decay of correlation shells, and shell drift. Comparison to results for the Lennard-Jones system indicates the generality of these mechanisms for dense overdamped liquids. We use dynamical density functional theory on the basis of the Rosenfeld functional with self interaction correction. Superadiabatic forces are analysed using a recent power functional approximation. The power functional yields a modified Einstein long-time self diffusion coefficient in good agreement with simulation data.
CRIS-Team WoS Importer:2022-06-10

Dynamic equilibria in supported ionic liquid phase (SILP) catalysis: in situ IR spectroscopy identifies [Ru(CO)xCly]n species in water gas shift catalysis - Bauer, Tanja; Stepic, Robert; Wolf, Patrick; Kollhoff, Fabian; Karawacka, Weronica; Wick, Christian; Haumann, Marco; Wasserscheid, Peter; Smith, David M.; Smith, Ana-Suncana; Libuda, Jörg (Catalysis: Science and Technology, 2018)
Ru-based supported ionic liquid phase (SILP) systems efficiently catalyze the low-temperature water-gas shift reaction (WGSR). While previous studies suggest that Ru-carbonyl species play an important role in the mechanism, detailed knowledge on the catalytically active species is still missing. To identify these carbonyl complexes, we apply in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with density functional theory (DFT). Investigations of an as-prepared [R(CO)3Cl2]2/ [C4C1C1Im]Cl/Al2O3 catalyst indicate splitting of the dimer induced by Cl−. Subsequently, an equilibrium between several [R(CO)xCly]n species is established, in which the IL serves as an effectively infinite Cl− reservoir. We find that the major species in the system freshly-prepared from [R(CO)3Cl2]2 is indeed [R(CO)3Cl3]−. A smaller amount of [R(CO)2Cl3]− and chloride-rich species [R(CO)2Cl4]2− or [RuCOCl4]2− are also found in the SILP. Similar Ru-carbonyl species are observed during carbonylation of RuCl3/ [C4C1C1Im]Cl/Al2O3, another potential WGSR catalyst. The response of [Ru(CO)3Cl2]2/[C4C1C1Im]Cl/Al2O3 to heating and/or CO dosing was probed in situ and the results confirm the presence of the equilibrium proposed above.
Keywords: SILP catalysis; in situ IR spectroscopy; [Ru(CO)xCly]n species

Dynamics of Dirac observables in canonical cosmological perturbation theory - Giesel, Kristina; Singh, Parampreet; Winnekens, David (Classical and Quantum Gravity, 2019)

Dynamics of Na clusters in/on insulating substrates - Bär, Matthias; Faber, Bernd; Reinhard, Paul-Gerhard; Dinh, P. M.; Suraud, E.; Wopperer, P. (Journal of Physics: Conference Series, 2010)
We apply a hierarchical model for Na clusters in/on insulating substrate (Ar or MgO) to explore three different regimes of cluster dynamics. The effect of the interface is scrutinized for optical response of Na8 embedded in Ar matrix and deposited on MgO(001) surface. The different mechanical properties of Ar and MgO surface are explored in studying the collision with a Na6 cluster at different initial energies. The stabilization of highly charged Na clusters through a substrate is discussed for strong laser ionization of Na8 in Ar matrix and on MgO surface. © 2010 IOP Publishing Ltd.
CRIS-Team Scopus Importer:2023-07-24

Dynamics of photodoped charge transfer insulators - Golez, Denis; Boehnke, Lewin; Eckstein, Martin; Werner, Philipp (Physical Review B, 2019)
We study the dynamics of charge transfer insulators after photoexcitation using the three-band Emery model and a nonequilibrium extension of Hartree-Fock + EDMFT (extended dynamical mean field theory) and GW + EDMFT. While the equilibrium properties are accurately reproduced by the Hartree-Fock treatment of the ligand bands, dynamical correlations are essential for a proper description of the photodoped state. Photodoping leads to a renormalization of the charge transfer gap and to a substantial broadening of the bands. We calculate the time-resolved photoemission spectrum and optical conductivity and find qualitative agreement with experiments. Our formalism enables the realistic description of nonequilibrium phenomena in materials with ligand bands. It provides a tool to explore the optical manipulation of interaction and correlation effects, including insulator-metal and magnetic transitions.
CRIS-Team WoS Importer:2019-08-02

Dynamics of Specific Vesicle-Substrate Adhesion: From Local Events to Global Dynamics - Reister-Gottfried, Ellen; Sengupta, Kheya; Lorz, Barbara Gertrud; Sackmann, Erich; Seifert, Udo; Smith, Ana-Suncana (Physical Review Letters, 2008)
We present a synergistic combination of simulations and experimental data on the dynamics of membrane adhesion. We show that a change in either the density or the strength of the bonds results in very different dynamics. Such behavior is explained by introducing an effective binding affinity that emerges as a result of the competition between the strength of the chemical bonds and the environment defined by the fluctuating membrane.
Keywords: MEMBRANES; CELLS; DIFFUSION; KINETICS; COMPLEX

Dynamic Structure Factor of Disordered Quantum Spin Ladders - Hörmann, Max; Wunderlich, Paul; Schmidt, Kai Phillip (Physical Review Letters, 2018)
We investigate the impact of quenched disorder on the zero-temperature dynamic structure factor of two leg quantum spin ladders. Using linked-cluster expansions and bond-operator mean-field theory, huge effects on individual quasiparticles but also on composite bound states arid two-quasiparticle continua are observed. This leads to intriguing quantum structures in dynamical conelation functions well observable in spectroscopic experiments.

Dynamic structure factor of Heisenberg bilayer dimer phases in the presence of quenched disorder and frustration - Hörmann, Max; Schmidt, Kai Phillip (Physical Review B, 2020)
We investigate the influence of quenched disorder on the dynamic structure factor of Heisenberg bilayers on the square, triangular, and kagome lattice in the quantum paramagnetic phase. Perturbative continuous unitary transformations and white graphs are employed to calculate the one-triplon contribution up to high orders in perturbation about the dimer limit for bimodal and continuous disorder. For the square lattice we find that the lifetime of the gap mode is increased by stronger quantum correlations, while stronger disorder effects are observed for the triangular lattice due to geometric frustration. For intradimer disorder, in-band energy gaps are observed for both lattices which can be understood in terms of a level repulsion on dimers with low and high intradimer exchange that are close in energy at the momentum where the in-band gap opens. For the highly frustrated kagome lattice disorder even decreases the gap energy. In addition, the localization length of the low-energy flat band is increased up to order 7 in perturbation theory. The interplay of quenched disorder, geometric frustration, and strong correlations leads therefore to rich structures in the dynamical structure factor of two-dimensional quantum magnets.
CRIS-Team WoS Importer:2020-10-09

Dynamic structure factor of the antiferromagnetic Kitaev model in large magnetic fields - Schellenberger, Andreas; Hörmann, Max; Schmidt, Kai Phillip (Physical Review B, 2022)
We investigate the dynamic structure factor of the antiferromagnetic Kitaev honeycomb model in a magnetic field by applying perturbative continuous unitary transformations about the high-field limit. One- and two-quasiparticle properties of the dressed elementary spin-flip excitations of the high-field polarized phase are calculated, which account for most of the spectral weight in the dynamic structure factor. We discuss the evolution of spectral features in these quasiparticle sectors in terms of one-quasiparticle dispersions, two-quasiparticle continua, the formation of antibound states, and quasiparticle decay. In particular, a comparably strong spectral feature above the upper edge of the upmost two-quasiparticle continuum represents three antibound states which form due to nearest-neighbor density-density interactions.
CRIS-Team Scopus Importer:2022-09-30

Easy and versatile coating approach for long-living white hybrid light-emitting diodes - Niklaus, Lukas; Dakhil, Haider; Kostrzewa, Monika Maria; Brana Coto, Pedro; Sonnewald, Uwe; Wierschem, Andreas; Costa Riquelme, Rubén Dario (Materials Horizons, 2016)
Herein, we provide a new easy-to-do protocol for preparing luminescent rubber-like materials based on a wide palette of compounds, such as small-molecules, quantum dots, polymers, and coordination complexes. The combination of this new protocol with that for preparing similar rubbers based on fluorescent proteins states the universal character of our approach. This is further assessed by using comprehensive spectroscopic and rheological investigations. Furthermore, the novel luminescent rubbers are applied as downconverting packing systems to develop white hybrid light-emitting diodes (WHLEDs), which are heralded as a solid alternative to achieve energy-saving, solid-state, and white-emitting sources in the coming future. As such, the current work also provides a clear prospect of this emerging lighting technology by means of a direct comparison among WHLEDs fabricated with all the above-mentioned down-converting systems. Here, the use of rubbers based on coordination complexes outperforms the others in terms of both luminous efficiency and colour quality with an unprecedented stability superior to 1000 h under continuous operation conditions. This represents an order of magnitude enhancement compared to the state-of-the-art WHLEDs, while keeping luminous efficiencies of around 100 lm W-1.

Effective adhesion strength of specifically bound vesicles - Smith, Ana-Suncana; Seifert, Udo (Physical Review E, 2005)
A theoretical approach has been undertaken in order to model the thermodynamic equilibrium of a 3D vesicle adhering to a flat substrate. The vesicle is treated in a canonical description with a fixed number of sites. A finite number of these sites are occupied by mobile ligands that are capable of interacting with a discrete number of receptors immobilized on the substrate. Explicit consideration of the bending energy of the vesicle shape has shown that the problem of the vesicle shape can be decoupled from the determination of the optimum allocation of ligands over the vesicle. The allocation of bound and free ligands in the vesicle can be determined as a function of the size of the contact zone, the ligand-receptor binding strength, and the concentration of the system constituents. Several approximate solutions for different regions of system parameters are determined and in particular, the distinction between receptor- and ligand-dominated equilibria is found to be important. The crossover between these two types of solutions is found to occur at a critical size of the contact zone. The presented approach enables the calculation of the effective adhesion strength of the vesicle and thus permits meaningful comparisons with relevant experiments as well as connecting the presented model with the proven success of the continuum approach for modeling the shapes of adhering vesicles. The behavior of the effective adhesion strength is analyzed in detail and several approximate expressions for it are given.
Keywords: CELL-ADHESION; SHAPE TRANSFORMATIONS; PHASE-SEPARATION; MEMBRANES; THERMODYNAMICS; COMPETITION; TRANSITION; REPULSION; STICKERS; MODELS

Effective crystal field and Fermi surface topology: A comparison of d- and dp-orbital models - Parragh, N.; Sangiovanni, Giorgio; Hansmann, Philipp; Hummel, S.; Held, Karsten; Toschi, Alessandro (Physical Review B, 2013)
The effective crystal field in multiorbital correlated materials can be either enhanced or reduced by electronic correlations with crucial consequences for the topology of the Fermi surface and, hence, on the physical properties of these systems. In this respect, recent local density approximation plus dynamical mean-field theory studies of Ni-based heterostructure have shown contradicting results, depending on whether the less correlated p orbitals are included or not. We investigate the origin of this problem and identify the key parameters controlling the Fermi surface properties of these systems. Without the p orbitals, the model is quarter-filled, while the d manifold moves rapidly towards half-filling when the p orbitals are included. This implies that the local Hund's exchange, while rather unimportant for the former case, can play a predominant role in controlling the orbital polarization for the extended basis set by favoring the formation of a larger local magnetic moment.
CRIS-Team WoS Importer:2020-02-19

Effective dynamics from coherent state path integral of full loop quantum gravity - Han, Muxin; Liu, Hongguang (Physical Review D, 2020)
A new routine is proposed to relate loop quantum cosmology (LQC) to loop quantum gravity (LQG) from the perspective of effective dynamics. We derive the big-bang singularity resolution and big bounce from the first principle of full canonical LQG. Our results are obtained in the framework of the reduced phase space quantization of LQG. As a key step in our work, we derive with coherent states a new discrete path integral formula of the transition amplitude generated by the physical Hamiltonian. The semiclassical approximation of the path integral formula gives an interesting set of effective equations of motion (EOMs) for full LQG. When solving the EOMs with homogeneous and isotropic ansatz, we reproduce the LQC effective dynamics in the mu(0)-scheme. The solution replaces the big-bang singularity by a big bounce. In the end, we comment on the possible relation between the (mu) over bar -scheme of effective dynamics and the continuum limit of the path integral formula.
CRIS-Team WoS Importer:2020-02-21

Effective Hamiltonian for liquid-vapor interfaces - Mecke, Klaus; et al. (Physical Review E, 1999)
Starting from a density functional theory for inhomogeneous fluids we derive an effective Hamiltonian for liquid-vapor interfaces of simple fluids which goes beyond the common phenomenological capillary-wave description. in contrast to other approaches we take into account the long-ranged power-law decay of the dispersion forces between the fluid particles which changes the functional form of the wave-vector-dependent surface tension qualitatively. In particular, we find two different forms of the bending rigidity for the capillary waves, a negative one for small wave vectors determined by the long-ranged dispersion forces and a positive rigidity for large wave vectors due to the distortions of the intrinsic density profile in the vicinity of the locally curved interface. The differences to the standard capillary-wave theory and the relevance of these results for the interpretation of scattering experiments are discussed.

Effective models for gapped phases of strongly correlated quantum lattice models - Yang, H. Y.; Schmidt, Kai Phillip (EPL - Europhysics Letters, 2011)
We present a robust scheme to derive effective models non-perturbatively for quantum lattice models when at least one degree of freedom is gapped. A combination of graph theory and the method of continuous unitary transformations (gCUTs) is shown to efficiently capture all zero-temperature fluctuations in a controlled spatial range. The gCUT can be used either for effective quasi-particle descriptions or for effective low-energy descriptions in case of infinitely degenerate subspaces. We illustrate the method for 1d and 2d lattice models yielding convincing results in the thermodynamic limit. We find that the recently discovered spin liquid in the Hubbard model on the honeycomb lattice lies outside the perturbative strong-coupling regime. Various extensions and perspectives of the gCUT are discussed. Copyright (C) EPLA, 2011

Effective spin couplings in the Mott insulator of the honeycomb lattice Hubbard model - Yang, Hong-Yu; Fabricio Albuquerque, A.; Capponi, Sylvain; Laeuchli, Andreas M.; Schmidt, Kai Phillip (New Journal of Physics, 2012)
Motivated by the recent discovery of a spin-liquid phase for the Hubbard model on the honeycomb lattice at half-filling (Meng et al 2010 Nature 88 487), we apply both perturbative and non-perturbative techniques to derive effective spin Hamiltonians describing the low-energy physics of the Mottinsulating phase of the system. Exact diagonalizations of the so-derived models on small clusters are performed, in order to assess the quality of the effective low-energy theory in the spin-liquid regime. We show that six-spin interactions on the elementary loop of the honeycomb lattice are the dominant sub-leading effective couplings. A minimal spin model is shown to reproduce most of the energetic properties of the Hubbard model on the honeycomb lattice in its spin-liquid phase. Surprisingly, a more elaborate effective low-energy spin model obtained by a systematic graph expansion rather disagrees beyond a certain point with the numerical results for the Hubbard model at intermediate couplings.

Effective Spin Model for the Spin-Liquid Phase of the Hubbard Model on the Triangular Lattice - Yang, Hong-Yu; Laeuchli, Andreas M.; Mila, Frederic; Schmidt, Kai Phillip (Physical Review Letters, 2010)
We show that the spin-liquid phase of the half-filled Hubbard model on the triangular lattice can be described by a pure spin model. This is based on a high-order strong coupling expansion ( up to order 12) using perturbative continuous unitary transformations. The resulting spin model is consistent with a transition from three-sublattice long-range magnetic order to an insulating spin-liquid phase, and with a jump of the double occupancy at the transition. Exact diagonalizations of both models show that the effective spin model is quantitatively accurate well into the spin-liquid phase, and a comparison with the Gutzwiller projected Fermi sea suggests a gapless spectrum and a spinon Fermi surface.

Effective substrate potentials with quasicrystalline symmetry depend on the size of the adsorbed particles - Rühle, Felix; Sandbrink, Matthias; Stark, Holger; Schmiedeberg, Michael (European Physical Journal E, 2015)
We explore the effective potential landscapes that extended particles experience when adsorbed on the surface of quasicrystals. Commonly, these are solids with long-ranged order but no translational symmetry. The effective potentials significantly depend on the size of the adsorbed particles. We show how changing the particle radius changes the so-called local isomorphism class of the effective quasicrystalline pattern. This means effective potentials for different particle sizes cannot directly be mapped onto each other. Our theoretical predictions are confirmed by Monte Carlo simulations. The results are important for colloidal particles with different sizes that are subjected to laser fields with quasicrystalline symmetry as well as for systems where extended molecules are deposited onto the surface of metallic quasicrystals.

Effective theory of lattice electrons strongly coupled to quantum electromagnetic fields - Li, Jiajun; Schamriß, Lukas; Eckstein, Martin (Physical Review B, 2022)
Recent experiments have revealed the tantalizing possibility of fabricating lattice electronic systems strongly coupled to quantum fluctuations of electromagnetic fields, e.g., by means of geometry confinement from a cavity or artificial gauge fields in quantum simulators. In this work, we develop a high-frequency expansion to construct the effective models for lattice electrons strongly coupled to a continuum of off-resonant photon modes with arbitrary dispersion. The theory is nonperturbative in the light-matter coupling strength and is therefore particularly suitable for the ultrastrong light-matter coupling regime. Using the effective models, we demonstrate how the dispersion and topology of the electronic energy bands can be tuned by the cavity. In particular, quasi-one-dimensional physics can emerge in a two-dimensional square lattice due to a spatially anisotropic band renormalization, and a topologically nontrivial anomalous quantum Hall state can be induced in a honeycomb lattice when the cavity setup breaks time-reversal symmetry. We also demonstrate that the photon-mediated interaction induces an unconventional superconducting paired phase distinct from the pair-density-wave state discussed in models with truncated light-matter coupling. Finally, we study a realistic setup of a Fabry-Pérot cavity. Our work provides a systematic framework to explore the emergent phenomena due to strong light-matter coupling and points out alternative directions of engineering orders and topological states in solids.
CRIS-Team Scopus Importer:2022-05-13

Effect of body deformability on microswimming - Pande, Jayant; Merchant, Laura; Krueger, Timm; Harting, Jens; Smith, Ana-Suncana (Soft Matter, 2017)
In this work we consider the following question: given a mechanical microswimming mechanism, does increased deformability of the swimmer body hinder or promote the motility of the swimmer? To answer this we run immersed-boundary-lattice-Boltzmann simulations of a microswimmer composed of deformable beads connected with springs. We find that the same deformations in the beads can result in different effects on the swimming velocity, namely an enhancement or a reduction, depending on the other parameters. To understand this we determine analytically the velocity of the swimmer, starting from the forces driving the motion and assuming that the deformations in the beads are known as functions of time and are much smaller than the beads themselves. We find that to the lowest order, only the driving frequency mode of the surface deformations contributes to the swimming velocity, and comparison to the simulations shows that both the velocity-promoting and velocity-hindering effects of bead deformability are reproduced correctly by the theory in the limit of small bead deformations. For the case of active deformations we show that there are critical values of the spring constant - which for a general swimmer corresponds to its main elastic degree of freedom - which decide whether the body deformability is beneficial for motion or not.
Keywords: LOW-REYNOLDS-NUMBER; LATTICE BOLTZMANN; SWIMMER; CILIA; PARTICLES; DYNAMICS; MOTORS; FLUIDS; SIMULATIONS; EFFICIENT

Effect of crystallization on the electronic and optical properties of archetypical porphyrins - Malcioglu, Osman; Bechis, Irene; Bockstedte, Michel Georg (Physical Chemistry Chemical Physics, 2020)
Thin porphyrin films as employed in modern optical devices or photovoltaic applications show deviating electronic and optical properties from the gasphase species. Any understanding of the physical origin may pave way to a specific engineering of these properties via ligand or substituent control. Here we investigate the impact of crystallization of prototypical porphyrins on the electronic levels and optical properties in the framework of density functional theory and many-body perturbation theory. Crystallization substantially shrinks the HOMO-LUMO gap based on polarization effects. We find a shift of the HOMO to higher energy is consistent with recent experiment of MgTPP multilayer film on Ag (100) [A. Classen et al., Phys. Rev. B, 2017, 95, 115414]. Calculated excitation spectra demonstrate a significant redshift of excitation bands except for the Q bands. These lowest excitation bands, in stark contrast to the strong HOMO-LUMO gap renormalization, remain essentially the same as in the gas phase. Our work underlines the possibility of band-gap engineering via ligand-controlled modification of the polarizability.
CRIS-Team WoS Importer:2020-03-27

Effect of loop quantization prescriptions on the physics of non-singular gravitational collapse - Giesel, Kristina; Li, Bao-Fei; Singh, Parampreet (The Sixteenth Marcel Grossmann Meeting, pp. 4267-4271 (2023), 2023)
We review recent developments in the physical implications of two loop quantization strategies for the interior of a homogeneous dust cloud. The first is the loop quantization with holonomies and the triads while the second is with holonomies and the gauge covariant fluxes. Although both of the quantization schemes resolve the classical central singularity regardless of the initial conditions, they also lead to a distinct phenomenology. For the first loop quantization, we find that when the dust mass is larger than a threshold value, both black hole and white hole would form and their evolution is symmetric with respect to the bounce point, leading to black hole-white hole twins. In contrast, in the second quantization, the evolution of the outermost dust shell is asymmetric with respect to the bounce point, and as a result the black hole-white hole twins can never form. Even in the situation when both black hole and white hole can form, the mass of the latter is only 2/π of the mass of the former.<br

Effect of nonadiabatic electronic-vibrational interactions on the transport properties of single-molecule junctions - Erpenbeck, André; Haertle, R.; Thoss, Michael (Physical Review B, 2015)
The interaction between electronic and vibrational degrees of freedom in single-molecule junctions may result from the dependence of the electronic energies or the electronic states of the molecular bridge on the nuclear displacement. The latter mechanism leads to a direct coupling between different electronic states and is referred to as nonadiabatic electronic-vibrational coupling. Employing a perturbative nonequilibrium Green’s function approach, we study the influence of nonadiabatic electronic-vibrational coupling in model molecular junctions. Thereby, we distinguish between systems with well-separated and quasidegenerate electronic levels. The results show that the nonadiabatic electronic-vibrational interaction can have a significant influence on the transport properties. The underlying mechanisms, in particular the difference between nonadiabatic and adiabatic electronic-vibrational couplings, are analyzed in some detail.

Effect of Structure and Disorder on the Charge Transport in Defined Self-Assembled Monolayers of Organic Semiconductors - Schmaltz, Thomas; Gothe, Bastian; Krause, Andreas; Leitherer, Susanne; Steinrück, Hans-Georg; Thoss, Michael; Clark, Timothy; Halik, Marcus (Acs Nano, 2017)
Self-assembled monolayer field-effect transistors (SAMFETs) are not only a promising type of organic electronic device but also allow detailed analyses of structure-property correlations. The influence of the morphology on the charge transport is particularly pronounced, due to the confined monolayer of 2D- extgreekp-stacked organic semiconductor molecules. The morphology, in turn, is governed by relatively weak van-der-Waals interactions and is thus prone to dynamic structural fluctuations. Accordingly, combining electronic and physical characterization and time-averaged X-ray analyses with the dynamic information available at atomic resolution from simulations allows us to characterize self-assembled monolayer (SAM) based devices in great detail. For this purpose, we have constructed transistors based on SAMs of two molecules that consist of the organic p-type semiconductor benzothieno[3,2-b][1]benzothiophene (BTBT), linked to a C11 or C12 alkylphosphonic acid. Both molecules form ordered SAMs; however, our experiments show that the size of the crystalline domains and the charge-transport properties vary considerably in the two systems. These findings were confirmed by molecular dynamics (MD) simulations and semiempirical molecular-orbital electronic-structure calculations, performed on snapshots from the MD simulations at different times, revealing, in atomistic detail, how the charge transport in organic semiconductors is influenced and limited by dynamic disorder.

Effects of a pulling force on the shape of a bound vesicle - Smith, Ana-Suncana; Sackmann, Erich; Seifert, Udo (EPL - Europhysics Letters, 2003)
We develop a theoretical model to describe the vertical pulling of vesicles adhered in a contact potential. For a range of applied forces, locally stable bound shapes, separated from the free shape by an energy barrier, can be found. The phase diagram contains regions with either a unique bound shape or an additional meta-stable shape. Upon pulling, these shapes unbind discontinuously since the vesicles disengage from the substrate while still possessing a finite adhesion area.
Keywords: MEMBRANE-MEMBRANE ADHESION; MOLECULAR CROSS-BRIDGES; SHEAR-FLOW; DETAILED MECHANICS; ADHERING VESICLES; LIFT FORCE; CELLS; SEPARATION; ENERGY; MODELS

Effects of domain walls in bilayer graphene in an external magnetic field - Baßler, Nico; Schmidt, Kai Phillip (Physical Review B, 2021)
We investigate bilayer graphene systems with layer switching domain walls separating the two energetically equivalent Bernal stackings in the presence of an external magnetic field. To this end, we calculate quantum transport and local densities of three microscopic models for a single domain wall: a hard wall, a defect due to shear, and a defect due to tension. The quantum transport calculations are performed with a recursive Green's function method. Technically, we discuss an explicit algorithm for the separation of a system into subsystems for the recursion and we present an optimization of the well known iteration scheme for lead self-energies for sparse chain couplings. We find strong physical differences for the three different types of domain walls in the integer quantum Hall regime. For a domain wall due to shearing of the upper graphene layer, there is a plateau formation in the magnetoconductance for sufficiently wide defect regions. For wide domain walls due to tension in the upper graphene layer, there is only an approximate plateau formation with fluctuations of the order of the elementary conductance quantum σ0. A direct transition between stacking regions like for the hard wall domain wall shows no plateau formation and is therefore not a good model for either of the previously mentioned extended domain walls.
CRIS-Team Scopus Importer:2021-05-21

Effects of frustration on the nonequilibrium dynamics of photoexcited lattice systems - Bittner, Nikolaj; Golez, Denis; Eckstein, Martin; Werner, Philipp (Physical Review B, 2020)
We theoretically investigate the effects of spin frustration on the nonequilibrium dynamics of photoexcited carriers in a half-filled two-dimensional Hubbard model. Using a nonequilibrium generalization of the dynamical cluster approximation, we compare the relaxation dynamics in lattices which interpolate between the triangular lattice and square lattice configuration. To clarify the influence of the density of states of the different lattices, we also consider the corresponding single-site dynamical mean-field theory results. Our study shows that the cooling effect resulting from the disordering of the spin background is less effective in the triangular case because of the frustration. This manifests itself in a longer relaxation time of the photodoped population, as measured by the time-resolved photoemission signal, and a higher effective temperature of the photodoped carriers in the nonthermal steady state after the intra-Hubbard-band thermalization.
CRIS-Team WoS Importer:2021-01-22

Efficiency at Maximum Power of a Carnot Quantum Information Engine - Fadler, Paul; Friedenberger, Alexander; Lutz, Eric (Physical Review Letters, 2023)
Optimizing the performance of thermal machines is an essential task of thermodynamics. We here consider the optimization of information engines that convert information about the state of a system into work. We concretely introduce a generalized finite-time Carnot cycle for a quantum information engine and optimize its power output in the regime of low dissipation. We derive a general formula for its efficiency at maximum power valid for arbitrary working media. We further investigate the optimal performance of a qubit information engine subjected to weak energy measurements.
CRIS-Team Scopus Importer:2023-08-04

Efficient Simulation of Loop Quantum Gravity: A Scalable Linear-Optical Approach - Cohen, Lior; Brady, Anthony J.; Huang, Zichang; Liu, Hongguang; Qu, Dongxue; Dowling, Jonathan P.; Han, Muxin (Physical Review Letters, 2021)
The problem of simulating complex quantum processes on classical computers gave rise to the field of quantum simulations. Quantum simulators solve problems, such as boson sampling, where classical counterparts fail. In another field of physics, the unification of general relativity and quantum theory is one of the greatest challenges of our time. One leading approach is loop quantum gravity (LQG). Here, we connect these two fields and design a linear-optical simulator such that the evolution of the optical quantum gates simulates the spin-foam amplitudes of LQG. It has been shown that computing transition amplitudes in simple quantum field theories falls into the bounded-error quantum polynomial time class, which strongly suggests that computing transition amplitudes of LQG are classically intractable. Therefore, these amplitudes are efficiently computable with universal quantum computers, which are, alas, possibly decades away. We propose here an alternative special-purpose linear-optical quantum computer that can be implemented using current technologies. This machine is capable of efficiently computing these quantities. This work opens a new way to relate quantum gravity to quantum information and will expand our understanding of the theory.
CRIS-Team Scopus Importer:2021-02-05

Elastic and Morphological Properties of Porous Biomaterials - Kapfer, Sebastian; Sporer, Susan; Hyde, Stephen T.; Mecke, Klaus; Schröder-Turk, Gerd (Biophysical Journal, 2010)

Elasticity of nematic phases with fundamental measure theory - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (Physical Review E, 2015)
In a previous publication [R. Wittmann, M. Marechal, and K. Mecke, Europhys. Lett. 109, 26003 (2015)], we introduced fundamental mixed measure theory (FMMT) for mixtures of anisotropic hard bodies, which shows that earlier results with an empirical parameter are inaccurate. Now we provide a deeper insight into the background of this theory in integral geometry. We study the Frank elastic coefficients in the nematic phase of the hard spherocylinder fluid. The framework of FMMT provides us with the required direct correlation function without additional input of an equation of state. A series representation of the mixed measure gives rise to closed analytical formulas for the elastic constants that only depend on the density, order parameters, and the particle geometry, pointing out a significant advantage of our geometry-based approach compared to other density functionals. Our elastic coefficients are in good agreement with computer simulations and increase with the density and the nematic order parameter. We confirm earlier mean-field predictions in the limits of low orientational order and infinitely long rods.

Electroluminescence: From White to Red: Electric-Field Dependent Chromaticity of Light-Emitting Electrochemical Cells based on Archetypal Porphyrins (Adv. Funct. Mater. 37/2016) - Weber, Michael; Wittmann, Judith; Burger, Alexandra; Malcioglu, Osman; Segarra-Martí, Javier; Hirsch, Andreas; Coto, Pedro B.; Bockstedte, Michel Georg; Costa, Ruben Dario (Advanced Functional Materials, 2016)
CRIS-Team Scopus Importer:2023-03-07
Keywords: collinear and vicinal regioisomers; electric-field dependent chromaticity; light-emitting electrochemical cells; tetraphenyl porphyrin; thin-film white-emitting sources

Electromagnetic coupling in tight-binding models for strongly correlated light and matter - Li, Jiajun; Golez, Denis; Mazza, Giacomo; Millis, Andrew J.; Georges, Antoine; Eckstein, Martin (Physical Review B, 2020)
We discuss the construction of low-energy tight-binding Hamiltonians for condensed-matter systems with a strong coupling to the quantum electromagnetic field. Such Hamiltonians can be obtained by projecting the continuum theory on a given set of Wannier orbitals. However, different representations of the continuum theory lead to different low-energy formulations because different representations may entangle light and matter, transforming orbitals into light-matter hybrid states before the projection. In particular, a multicenter Power-Zienau-Woolley transformation yields a dipolar Hamiltonian which incorporates the light-matter coupling via both Peierls phases and a polarization density. We compare this dipolar gauge Hamiltonian and the straightforward Coulomb gauge Hamiltonian for a one-dimensional solid to describe subcycle light-driven electronic motion in the semiclassical limit and a coupling of the solid to a quantized cavity mode which renormalizes the band-structure into electron-polariton bands. Both descriptions yield the same result when many bands are taken into account but the dipolar Hamiltonian is more accurate when the model is restricted to few electronic bands, while the Coulomb Hamiltonian requires fewer electromagnetic modes.
CRIS-Team WoS Importer:2020-06-05

Electronic and fluctuation dynamics following a quench to the superconducting phase - Stahl, Christopher; Eckstein, Martin (Physical Review B, 2021)
We investigate the dynamics of superconducting fluctuations in the attractive three-dimensional Hubbard model after a quench from the disordered phase to the ordered regime. While the long-time evolution is well understood in terms of dissipative time-dependent Ginzburg-Landau models with unstable potentials, early times are more demanding due to the inseparable dynamics of the pairing fluctuations and the electronic quasiparticles. Our simulation using the time-dependent fluctuation exchange approximation treats both degrees of freedom on the same footing and reveals a nonthermal electronic regime causing a nonmonotonous growth of the fluctuations. This feature is not directly captured by the Ginzburg-Landau theory but nevertheless remains observable beyond the thermalization time of the electrons. We further explore how the growth of the order parameter fluctuations leads to an opening of a pseudogap in the electronic spectrum and identify Andreev reflections as the dominant mechanism behind the gap opening.
CRIS-Team Scopus Importer:2021-02-12

Electronic Coherence and Coherent Dephasing in the Optical Control of Electrons in Graphene - Heide, Christian; Eckstein, Timo; Boolakee, Tobias; Gerner, Constanze; Weber, Heiko B.; Franco, Ignacio; Hommelhoff, Peter (Nano Letters, 2021)
Electronic coherence is of utmost importance for the access and control of quantum-mechanical solid-state properties. Using a purely electronic observable, the photocurrent, we measure a lower bound of the electronic coherence time of 22 ± 4 fs in graphene. The photocurrent is ideally suited to measure electronic coherence, as it is a direct result of coherent quantum-path interference, controlled by the delay between two ultrashort two-color laser pulses. The maximum delay for which interference between the population amplitude injected by the first pulse interferes with that generated by the second pulse determines the electronic coherence time. In particular, numerical simulations reveal that the experimental data yields a lower bound on the electronic coherence time, masked by coherent dephasing due to the broadband absorption in graphene. We expect that our results will significantly advance the understanding of coherent quantum control in solid-state systems ranging from excitation with weak fields to strongly driven system
Keywords: graphene; quantum-path interference; electronic coherence time; quantum control

Electronic correlations in V2O3 studied with K-edge X-ray absorption spectroscopy - Rodolakis, Fanny; Hansmann, Philipp; Rueff, J-P; Toschi, Alessandro; Haverkort, M. W.; Sangiovanni, G.; Held, K.; Sikora, Marcin; Congeduti, A.; Itie, J-P; Baudelet, F.; Metcalf, P.; et al. (14TH INTERNATIONAL CONFERENCE ON X-RAY ABSORPTION FINE STRUCTURE (XAFS14), PROCEEDINGS, 2009)
CRIS-Team WoS Importer:2020-02-19

Electronic structure of nickelates: From two-dimensional heterostructures to three-dimensional bulk materials - Hansmann, Philipp; Toschi, Alessandro; Yang, Xiaoping; Andersen, O. K.; Held, Karsten (Physical Review B, 2010)
Reduced dimensionality and strong electronic correlations, which are among the most important ingredients for cupratelike high-T-c superconductivity, characterize also the physics of nickelate-based heterostructures. Starting from the local-density approximation we arrive at a simple two-band model for quasi-two-dimensional (2D) LaNiO3/LaAlO3 heterostructures and extend it by introducing an appropriate hopping in the z direction to describe the dimensional crossover to three dimensions (3D). Using dynamical mean-field theory, we study the effects of electronic correlations with increasing interaction strength along the crossover from 2D to 3D. Qualitatively, the effects of electronic correlations are surprisingly similar, albeit quantitatively larger interaction strengths are required in three dimensions for getting a Mott-Hubbard insulating state. The exchange parameters of an effective Kugel-Khomskii-type spin-orbital model are also derived and reveal strong antiferromagnetic tendencies.
CRIS-Team WoS Importer:2020-02-19

Electronic structure of tetraphenylporphyrin layers on Ag(100) - Classen, Andrej; Pöschel, Rebecca; di Filippo, Gianluca; Fauster, Thomas; Malcioglu, Osman; Bockstedte, Michel Georg (Physical Review B, 2017)

ELINAS Schriftenreihe - Lubkoll, Christine; Mecke, Klaus; Heydenreich, Aura (De Gruyter, 2015)
DIE REIHE: LITERATUR- UND NATURWISSENSCHAFTEN entsteht unter Federführung des Erlanger Forschungszentrums für Literatur- und Naturwissenschaften (ELINAS). Experten unterschiedlicher Fachkulturen führen darin ihre Methoden zusammen und fragen sowohl nach den Funktionen der Sprache in der naturwissenschaftlichen Forschung als auch nach den Verfahren der Modellierung naturwissenschaftlicher Erkenntnisse in der Literatur. Die Reihe versteht sich als ein interdisziplinäres Forum zur Reflexion der kulturellen Bedeutung natur- und literaturwissenschaftlicher Forschung sowie zur Ethik und Rhetorik wissenschaftlicher Argumentatio

Emergence of a 2d macro-spin liquid in a highly frustrated 3d quantum magnet - Sikkenk, Tycho S.; Coester, Kris; Buhrandt, Stefan; Fritz, Lars; Schmidt, Kai Phillip (Physical Review B, 2017)
The classical Ising model on the frustrated three-dimensional (3D) swedenborgite lattice has disordered spin liquid ground states for all ratios of inter- and intraplanar couplings. Quantum fluctuations due to a transverse field give rise to several exotic phenomena. In the limit of weakly coupled kagome layers we find a 3D version of disorder by disorder degeneracy lifting. For large out-of-plane couplings one-dimensional macrospins are formed, which realize a disordered macrospin liquid phase on an emerging two-dimensional triangular lattice. We speculate about a possibly exotic version of quantum criticality that connects the polarized phase to the macrospin liquid.

Emergent de Sitter epoch of the loop quantum cosmos: A detailed analysis - Assanioussi, Mehdi; Dapor, Andrea; Liegener, Klaus; Pawlowski, Tomasz (Physical Review D, 2019)
We present a detailed analysis of a quantum model for loop quantum cosmology based on strict application of the Thiemann regularization algorithm for the Hamiltonian in loop quantum gravity, extending the results presented previously in our brief report. This construction leads to a qualitative modification of the bounce paradigm. Quantum gravity effects still lead to a quantum bounce connecting deterministically large classical universes. However, the evolution features a large epoch of de Sitter Universe, with emergent cosmological constant of Planckian order, smoothly transiting into a spatially flat expanding universe. Moreover, we present an effective Hamiltonian describing the quantum evolution to high accuracy and for which the dynamics can be solved analytically.
CRIS-Team WoS Importer:2019-10-18

Emergent fermions and anyons in the Kitaev model - Schmidt, Kai Phillip; Dusuel, Sebastien; Vidal, Julien (Physical Review Letters, 2008)
We study the gapped phase of the Kitaev model on the honeycomb lattice using perturbative continuous unitary transformations. The effective low-energy Hamiltonian is found to be an extended toric code with interacting anyons. High-energy excitations are emerging free fermions which are composed of hard-core bosons with an attached string of spin operators. The excitation spectrum is mapped onto that of a single particle hopping on a square lattice in a magnetic field. We also illustrate how to compute correlation functions in this framework. The present approach yields analytical perturbative results in the thermodynamical limit without using the Majorana or the Jordan-Wigner fermionization initially proposed to solve this problem.

Emergent four-dimensional linearized gravity from a spin foam model - Han, Muxin; Huang, Zichang; Zipfel, Antonia (Physical Review D, 2019)
Spin foam models (SFMs) are covariant formulations of loop quantum gravity (LQG) in four dimensions. This work studies the perturbations of SFMs on a flat background. It demonstrates for the first time that smooth curved spacetime geometries satisfying the Einstein equation can emerge from discrete SFMs under an appropriate low energy limit, which corresponds to a semiclassical continuum limit of SFMs. In particular, we show that the low energy excitations of SFMs on a flat background give all smooth solutions of linearized Einstein equations (spin-2 gravitons). This indicates that at the linearized level, classical Einstein gravity can arise as a low energy effective theory from SFMs. Thus our result heightens the confidence that covariant LQG is a consistent theory of quantum gravity. As a key technical tool, a regularization/deformation of the SFM is employed in the derivation. The deformation parameter delta becomes a coupling constant of a higher curvature correction term to Einstein gravity from SFM.
CRIS-Team WoS Importer:2019-08-09

Energy equipartition and minimal radius in entropic gravity - Sahlmann, Hanno (Physical Review D - Particles, Fields, Gravitation and Cosmology, 2011)
In this article, we investigate the assumption of equipartition of energy in arguments for the entropic nature of gravity. It has already been pointed out by other authors that equipartition is not valid for low temperatures. Here we additionally point out that it is similarly not valid for systems with bounded energy. Many explanations for black hole entropy suggest that the microscopic systems responsible have a finite dimensional state space, and thus finite maximum energy. Assuming this to be the case leads to drastic corrections to Newton's law for high gravitational fields, and, in particular, to a singularity in acceleration at finite radius away from a point mass. This is suggestive of the physics at the Schwarzschild radius. We show, however, that the location of the singularity scales differently. © 2011 American Physical Society.

Energy landscape description of the clustering transition for active soft spheres - Maiti, Moumita; Schmiedeberg, Michael (EPL - Europhysics Letters, 2019)
For a system consisting of active soft spheres in three dimensions, we study the transition from a fluid where overlaps between particles can only occur for a short time after a collision to a state where clusters of overlapping particles persist for a long time. In order to determine the properties of the transition, we explore the energy landscape of the system in a similar way as it is done for the determination of the athermal or thermal jamming transition. Note that for zero temperature the competition of particles that attach to existing clusters and particles that detach due to thermal effects does not arise. Therefore, here we do not study such a competition because we consider systems at small or zero energy. Instead, we explore at which packing fractions and what activities cluster formation can occur at all. In case of an athermal system the transition between systems where no clusters develop at all and systems where stable clusters are found is a first order transition for packing fractions below 0.55 while the transition is continuous in case of larger packing fractions. In case of thermal systems the transition is continuous everywhere. While our approach does not deal with the real dynamics of the system, it reveals the nature of the clustering transition and it enables a deeper insight in the consequences of thermal fluctuations and the relation of the clustering transition to jamming. Though Brownian timescales diverge in athermal systems, the activity that we consider can be compared to the active velocity in other simulations if the later is measured in units of the particle size divided by an elastic time scale.<br
Keywords: active particles clustering transition jamming

Engineering photon-mediated long-range spin interactions in Mott insulators - Fadler, Paul; Schmidt, Kai Phillip; Li, Jiajun; Eckstein, Martin (Physical Review B, 2024)
We investigate the potential to induce long-range spin interactions in a Mott insulator via the quantum electromagnetic field of a cavity. The coupling between light and spins is inherently nonlinear, and occurs via multiphoton processes like Raman scattering and two-photon absorption and emission with electronically excited intermediate states. Based on this, two pathways are elucidated: (i) In the absence of external driving, long-range interactions are mediated by the exchange of at least two virtual cavity photons. We show that these vacuum-mediated interactions can surpass local Heisenberg interactions in mesoscopic setups such as sufficiently small split-ring resonators. (ii) In a laser-driven cavity, interactions can be tailored through a hybrid scheme involving both external laser photons and cavity photons. This offers a versatile pathway for Floquet engineering of long-range interactions in macroscopic systems. In general, the derivation of these interactions requires careful consideration: Notably, we demonstrate that a simple phenomenological approach, based on a spin-photon Hamiltonian that captures Raman and two-photon processes with effective matrix elements, can be used only if the cavity is resonantly driven. Outside of these narrow resonant regimes as well as for the undriven case, a fourth-order series expansion within the underlying electronic model is necessary, which we perform to obtain long-range four-spin interactions in the half-filled Hubbard model.
CRIS-Team Scopus Importer:2024-03-15

Entanglement continuous unitary transformations - Sahin, Serkan; Schmidt, Kai Phillip; Orus, Roman (EPL - Europhysics Letters, 2017)
Continuous unitary transformations are a powerful tool to extract valuable information out of quantum many-body Hamiltonians, in which the so-called flow equation transforms the Hamiltonian to a diagonal or block-diagonal form in second quantization. Yet, one of their main challenges is how to approximate the infinitely-many coupled differential equations that are produced throughout this flow. Here we show that tensor networks offer a natural and non-perturbative truncation scheme in terms of entanglement. The corresponding scheme is called "entanglement-CUT" or eCUT. It can be used to extract the low-energy physics of quantum many-body Hamiltonians, including quasiparticle energy gaps. We provide the general idea behind eCUT and explain its implementation for finite 1d systems using the formalism of matrix product operators. We also present proof-of-principle results for the spin-(1/2) 1d quantum Ising model and the 3-state quantum Potts model in a transverse field. Entanglement-CUTs can also be generalized to higher dimensions and to the thermodynamic limit. Copyright (C) EPLA, 2017

Entanglement entropy from entanglement contour: Higher dimensions - Han, Muxin; Wen, Qiang (SciPost Physics Core, 2022)
We study the entanglement contour and partial entanglement entropy (PEE) in quantum field theories in 3 and higher dimensions. The entanglement entropy is evaluated from a certain limit of the PEE with a geometric regulator. In the context of the entanglement contour, we classify the geometric regulators, study their difference from the UV regulators. Furthermore, for spherical regions in conformal field theories (CFTs) we find the exact relation between the UV and geometric cutoff, which clarifies some subtle points in the previous literature. We clarify a subtle point of the additive linear combination (ALC) proposal for PEE in higher dimensions. The subset entanglement entropies in the ALC proposal should all be evaluated as a limit of the PEE while excluding a fixed class of local-short-distance correlation. Unlike the 2-dimensional configurations, naively plugging the entanglement entropy calculated with a UV cutoff will spoil the validity of the ALC proposal. We derive the entanglement contour function for spherical regions, annuli and spherical shells in the vacuum state of general-dimensional CFTs on a hyperplane.
CRIS-Team Scopus Importer:2022-06-03

Entropic torque - Mecke, Klaus; et al. (Physical Review Letters, 2002)
Quantitative predictions are presented of a depletion-induced torque and force acting on a single colloidal hard rod immersed in a solvent of hard spheres close to a planar hard wall. This torque and force, which are entirely of entropic origin, may play an important role for the key-lock principle, according to which a biological macromolecule (the key) is functional only in a particular orientation with respect to a cavity (the lock).

Entropy calculation for a toy black hole - Sahlmann, Hanno (Classical and Quantum Gravity, 2008)
In this paper, we carry out the counting of states for a black hole in loop quantum gravity, assuming however an equidistant area spectrum. We find that this toy-model is exactly solvable, and we show that its behavior is very similar to that of the correct model. Thus this toy-model can be used as a nice and simplifying 'laboratory' for questions about the full theory. © 2008 IOP Publishing Ltd.

Entropy-cooled nonequilibrium states of the Hubbard model - Werner, Philipp; Li, Jiajun; Golez, Denis; Eckstein, Martin (Physical Review B, 2019)
We show that the recently proposed cooling-by-doping mechanism allows one to efficiently prepare interesting nonequilibrium states of the Hubbard model. Using nonequilibrium dynamical mean field theory and a particle-hole symmetric setup with dipolar excitations to full and empty bands we produce cold photodoped Mott insulating states with a sharp Drude peak in the optical conductivity, a superconducting state in the repulsive Hubbard model with an inverted population, and eta-paired states in systems with a large density of doublons and holons. The reshuffling of entropy into full and empty bands not only provides an efficient cooling mechanism, it also allows one to overcome thermalization bottlenecks and slow dynamics that have been observed in systems cooled by the coupling to boson baths.
CRIS-Team WoS Importer:2019-10-25

Entropy of unimodular lattice triangulations - Mecke, Klaus; Krüger, Benedikt; Reinhard, Johannes (EPL - Europhysics Letters, 2015)
Triangulations are important objects of study in combinatorics, finite element simulations and quantum gravity, where their entropy is crucial for many physical properties. Due to their inherent complex topological structure even the number of possible triangulations is unknown for large systems. We present a novel algorithm for an approximate enumeration which is based on calculations of the density of states using the Wang-Landau flat histogram sampling. For triangulations on two-dimensional integer lattices we achieve excellent agreement with known exact numbers of small triangulations as well as an improvement of analytical calculated asymptotics. The entropy density is C = 2.196(3) consistent with rigorous upper and lower bounds. The presented numerical scheme can easily be applied to other counting and optimization problems. Copyright (C) EPLA, 2015

Ergodicity breaking transition in a glassy soft sphere system at small but non-zero temperatures - Maiti, Moumita; Schmiedeberg, Michael (Scientific Reports, 2018)

Erratum: Finding auxetic frameworks in periodic tessellations - Mitschke, Holger; Schwerdtfeger, Jan; Schury, Fabian; Stingl, Michael; Körner, Carolin; Singer, Robert; Robins, Vanessa; Mecke, Klaus; Schröder-Turk, Gerd (Advanced Materials, 2011)

Establishing conditions for simulating hydrophobic solutes in electric fields by molecular dynamics Effects of the long-range van der Waals treatment on the apparent particle mobility - Milicevic, Zoran; Marrink, Siewert J.; Smith, Ana-Suncana; Smith, David M. (Journal of Molecular Modeling, 2014)
Despite considerable effort over the last decade, the interactions between solutes and solvents in the presence of electric fields have not yet been fully understood. A very useful manner in which to study these systems is through the application of molecular dynamics (MD) simulations. However, a number of MD studies have shown a tremendous sensitivity of the migration rate of a hydrophobic solute to the treatment of the long range part of the van der Waals interactions. While the origin of this sensitivity was never explained, the mobility is currently regarded as an artifact of an improper simulation setup. We explain the spread in observed mobilites by performing extensive molecular dynamics simulations using the GROMACS software package on a system consisting of a model hydrophobic object (Lennard-Jones particle) immersed in water both in the presence and absence of a static electric field. We retrieve a unidirectional field-induced mobility of the hydrophobic object when the forces are simply truncated. Careful analysis of the data shows that, only in the specific case of truncated forces, a non-zero van der Waals force acts, on average, on the Lennard-Jones particle. Using the Stokes law we demonstrate that this force yields quantitative agreement with the field-induced mobility found within this setup. In contrast, when the treatment of forces is continuous, no net force is observed. In this manner, we provide a simple explanation for the previously controversial reports.
Keywords: Molecular dynamics; Electrophoretic mobility; Van der Waals interactions; GROMACS

eta-paired superconducting hidden phase in photodoped Mott insulators - Li, Jiajun; Golez, Denis; Werner, Philipp; Eckstein, Martin (Physical Review B, 2020)
We show that a metastable eta-pairing superconducting phase can be induced by photodoping doublons and holes into a strongly repulsive fermionic Hubbard model. The doublon-hole condensate originates from an intrinsic doublon-hole exchange interaction and does not rely on the symmetry of the half-filled Hubbard model. It extends over a wide range of doublon densities and effective temperatures. Different nonequilibrium protocols to realize this state are proposed and numerically tested. We also study the optical conductivity in the superconducting phase, which exhibits ideal metallic behavior, i.e., a delta function at zero frequency in the conductivity, in conjunction with a negative conductivity at large frequencies. These characteristic optical properties can provide a fingerprint of the eta-pairing phase in pump-probe experiments.
CRIS-Team WoS Importer:2020-11-06

EULER CHARACTERISTIC AND RELATED MEASURES FOR RANDOM GEOMETRIC SETS - Mecke, Klaus; et al. (Journal of Statistical Physics, 1991)
By an elementary calculation we obtain the exact mean values of Minkowksi functionals for a standard model of percolating sets. In particular, a recurrence theorem for the mean Euler characteristic recently put forward is shown to be incorrect. Related previous mathematical work is mentioned. We also conjecture bounds for the threshold density of continuum percolation, which are associated with the Euler characteristic.
Keywords: RANDOM SETS; INTEGRAL GEOMETRY; MINKOWSKI FUNCTIONALS; EULER CHARACTERISTIC; CONTINUUM PERCOLATION

Euler-Poincare characteristics of classes of disordered media - Mecke, Klaus; et al. (Physical Review E, 2001)
We consider a family of statistical measures based on the Euler-Poincare characteristic of It-dimensional space that are sensitive to the morphology of disordered structures. These measures embody information from ever?, order of the correlation function but can be calculated simply by summing over local contributions. We compute the evolution of the measures with density for a range of disordered microstructural models; particle-based models, amorphous microstructures, and cellular and foamlike structures. Analytic results for the particle-based models are given and the computational algorithm verified. Computational results for the different microstructures exhibit a range of qualitative behavior. A length scale is derived based on two-point autocorrelation functions to allow qualitative comparison between the different structures. We compute the morphological parameters for the experimental microstructure of a sandstone sample and compare them to three common stochastic model systems for porous media. None of the statistical models are able to accurately reproduce the morphology of the sandstone.

Evaluating the predictive character of the method of constrained geometries simulate external force with density functional theory - Wick, Christian; Topraksal, Ece; Smith, David M.; Smith, Ana-Suncana (Forces in Mechanics, 2022)
Mechanochemistry is a fast-developing field of interdisciplinary research with a growing number of applications. Therefore, many theoretical methods have been developed to quickly predict the outcome of mechanically induced reactions. Constrained geometries simulate External Force (CoGEF) is one of the earlier methods in this field. It is easily implemented and can be conducted with most DFT codes. However, recently, we observed totally different predictions for model systems of epoxy resins in different conformations and with different density functionals. To better understand the conformational and functional dependence in typical CoGEF calculations we present a systematic evaluation of the CoGEF method for different model systems covering homolytic and heterolytic bond cleavage reactions, electrocyclic ring opening reactions and scission of non-covalent interactions in hydrogen-bond complexes. From our calculations we observe that many mechanochemical descriptors strongly depend on the functional used, however, a systematic trend exists for the relative maximum Force. In general, we observe that the CoGEF procedure is forcing the system to high energetic regions on the molecular potential energy profiles, which can lead to unexpected and uncorrelated predictions of mechanochemical reactions. This is questioning the true predictive character of the method.
CRIS-Team Scopus Importer:2022-11-25
Keywords: COGEF; Density Functional Theory (DFT); Mechanical bond scission; Mechanical force; Mechanochemistry; Mechanoradicals; Molecular fracture

Event-chain Monte Carlo simulations of the liquid to solid transition of two-dimensional decagonal colloidal quasicrystals - Martinsons, Miriam; Hielscher, Johannes; Kapfer, Sebastian; Schmiedeberg, Michael (Journal of Physics: Condensed Matter, 2019)
In event-chain Monte Carlo simulations, we model colloidal particles in two dimensions that interact according to an isotropic short-ranged pair potential which supports the two typical length scales present in decagonal quasicrystals. We investigate the assembled structures as we vary the density and temperature. Our special interest is related to the transition from quasicrystal to liquid. In contrast to the KTHNY melting theory for quasicrystals which predicts an intermediate pentahedratic phase, we find a one-step first-order melting transition. However, we discover that the slow relaxation of phasonic flips, i.e. rearrangements of the particles due to additional degrees of freedom in quasicrystals, changes the positional correlation functions, to the extent that structures with long-range orientational correlations, but exponentially decaying positional correlations, are observe
Keywords: quasicrystal; event-chain Monte Carlo; melting

Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements - Mecke, Klaus; et al. (Proceedings of the National Academy of Sciences of the United States of America, 2005)
The hairy attachment system on a gecko's toes, consisting of one billion spatulae in the case of Gekko gecko [Ruibal, R. & Ernst, V. (1965) J. Morphol. 117, 271-294], allows it to adhere to nearly all surface topographies. The mechanistic basis for gecko adhesion has been intensely investigated, but the lowest hierarchical level, that of the spatula, has become experimentally accessible only recently. This report details measurements of the adhesion force exerted by a single gecko spatula for various atmospheric conditions and surface chemistries. Through judicious choice and modification of substrates, the short- and long-range adhesive forces are separated. In contrast to previous work [Autumn, K., Sitti, M., Liang, Y. C. A., Peattie, A. M., Hansen, W. R., Sporberg, S., Kenny, T. W., Fearing, R., Israelachvili, J. N. & Full, R. J. (2002) Proc. Nati. Acad. Sci. USA 99, 12252-12256], our measurements clearly show that humidity contributes significantly to gecko adhesion on a nanoscopic level. These findings are crucial for the development of artificial biomimetic attachment systems.
Keywords: capillary forces; van der Waals forces; Hamaker constant

Evidence for Charge-Transfer Mediation in the Primary Events of Singlet Fission in a Weakly Coupled Pentacene Dimer - Basel, Bettina; Zirzlmeier, Johannes; Hetzer, Constantin; Seelam, Rajagopala Reddy; Phelan, Brian T.; Krzyaniak, Matthew D.; Volland, Michel; Brana Coto, Pedro; Young, Ryan M.; Clark, Timothy; Thoss, Michael; Tykwinski, Rik; et al. (Chem, 2018)
Singlet fission (SF) is a process that converts one singlet excited state into two triplet states. The mechanism of SF is still not well understood. Here, we report on the use of a combination of transient absorption and electron paramagnetic resonance spectroscopies in conjunction with theoretical calculations to probe SF in a pentacene dimer linked by a non-conjugated, 1,4-diethynylbicyclo[2.2.2]octane spacer. Next to observing the key intermediates in solution-based SF, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons, we demonstrate that the coupling is sufficiently weak that SF is essentially inoperative in non-polar media. Transitioning to a polar medium, however, amplifies the coupling strength such that SF becomes operative and supports long triplet lifetimes. Our results offer strong evidence for a charge-transfer mediation and, in turn, provide a solid framework for decoding the complete mechanism of SF in systems beyond pentacene.

Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C9H18N2CuBr4 - Hong, Tao; Ying, Tao; Huang, Qing; Dissanayake, Sachith E.; Qiu, Yiming; Turnbull, Mark M.; Podlesnyak, Andrey A.; Wu, Yan; Cao, Huibo; Liu, Yaohua; Umehara, Izuru; Gouchi, Jun; et al. (Nature Communications, 2022)
There is a class of quantum phase transitions that do not fit into the traditional Landau paradigm, but are described in terms of fractionalized degrees of freedom and emergent gauge fields. Hong et al. find evidence of such a transition in a molecular spin-1/2 antiferromagnetic ladder compound under hydrostatic pressure.
CRIS-Team WoS Importer:2022-06-17

Evolution in quantum causal histories - Hawkins, Eli; Markopoulou, Fotini; Sahlmann, Hanno (Classical and Quantum Gravity, 2003)
We provide a precise definition and analysis of quantum causal histories (QCHs). A QCH consists of a discrete, locally finite, causal pre-spacetime with matrix algebras encoding the quantum structure at each event. The evolution of quantum states and observables is described by completely positive maps between the algebras at causally related events. We show that this local description of evolution is sufficient and that unitary evolution can be recovered wherever it should actually be expected. This formalism may describe a quantum cosmology without an assumption of global hyperbolicity; it is thus more general than the Wheeler-De Witt approach. The structure of a QCH is also closely related to quantum information theory and algebraic quantum field theory on a causal set.

Evolution of the electronic structure of a Mott system across its phase diagram: X-ray absorption spectroscopy study of (V1-xCrx)(2)O-3 - Rodolakis, Fanny; Rueff, J. -P.; Sikora, Marcin; Alliot, I.; Itie, J. -P.; Baudelet, F.; Ravy, Sylvain; Wzietek, Pawel; Hansmann, Philipp; Toschi, Alessandro; Haverkort, M. W.; Sangiovanni, Giorgio; et al. (Physical Review B, 2011)
V2O3 is an archetypal system for the study of correlation-induced, Mott-Hubbard metal-insulator transitions. Despite decades of extensive investigations, the accurate description of its electronic properties remains an open problem in the physics of strongly correlated materials, also because of the lack of detailed experimental data on its electronic structure over the whole phase diagram. We present here a high-resolution x-ray absorption spectroscopy study at the V K edge of (V1-xCrx)(2)O-3 to probe its electronic structure as a function of temperature, doping, and pressure, providing an accurate picture of the electronic changes over the whole phase diagram. We also discuss the relevance of the parallel evolution of the lattice parameters, determined with x-ray diffraction. This allows us to draw two conclusions of general interest: First, the transition under pressure presents peculiar properties, related to a more continuous evolution of the lattice and electronic structure; second, the lattice mismatch is a good parameter describing the strength of the first-order transition, and is consequently related to the tendency of the system toward the coexistence of different phases. Our results show that the evolution of the electronic structure while approaching a phase transition, and not only while crossing it, is also a key element to unveil the underlying physical mechanisms of Mott materials.
CRIS-Team WoS Importer:2020-02-19

Exact ground states of a spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice in a magnetic field - Verkholyak, Taras; Strecka, Jozef; Mila, Frederic; Schmidt, Kai Phillip (Physical Review B, 2014)
Exact ground states of a spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice with Heisenberg intradimer and Ising interdimer couplings are found by two independent rigorous procedures. The first method uses a unitary transformation to establish a mapping correspondence with an effective classical spin model, while the second method relies on the derivation of an effective hard-core boson model by continuous unitary transformations. Both methods lead to equivalent effective Hamiltonians providing a convincing proof that the spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice exhibits a zero-temperature magnetization curve with just two intermediate plateaus at one-third and one-half of the saturation magnetization, which correspond to stripe and checkerboard orderings of singlets and polarized triplets, respectively. The nature of the remarkable stripe order relevant to the one-third plateau is thoroughly investigated with the help of the corresponding exact eigenvector. The rigorous results for the spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice are compared with the analogous results for the purely classical Ising and fully quantum Heisenberg models. Finally, we discuss to what extent the critical fields of SrCu2(BO3)(2) and (CuCl)Ca2Nb3O10 can be described within the suggested Ising-Heisenberg model.

Exact moments of curvature measures in the Boolean model - Mecke, Klaus (Journal of Statistical Physics, 2001)
Curvature measures are important for the characterization of spatial structures since many physical phenomena depend essentially on the geometry of spatial configurations. Curvature-weighted correlation functions can be defined and calculated explicitly within the Boolean model. This standard model in statistical physics generates random geometries by overlapping grains (spheres, sticks) each with arbitrary location and orientation. A general decomposition relation for characteristic functions of submanifolds based on Chern's differential kinematic formula is used to obtain exact expressions for mean values and second order moments of curvature integrals, i.e., of Minkowski functionals. Am exact relation for the canonical and grand-canonical second-order moments of the morphological Minkowski measures can be derived based only on thermodynamic arguments. The results are applied on the morphological thermodynamics of complex fluids where specific heats are expressed in terms of curvature moments.
Keywords: random sets; integral geometry; Minkowski functionals; Euler characteristic; Boolean model

Exact plaquette singlet phases in an orthogonal-plaquette model - Boos, Carolin; Schmidt, Kai Phillip (Physical Review B, 2020)
We introduce a quantum spin-1/2 model hosting two exact plaquette singlet ground states in extended parameter regimes. There is an exact phase transition between both phases, at which the system has an extensive ground-state degeneracy. Further, the model exhibits an extensive number of conserved quantities, which allow the prediction of additional phases. We exploit this feature and explore the phase diagram in detail for two specific parameter regimes. The model is based solely on Heisenberg interactions and seems sufficiently simple to be realized in quantum materials. A general scheme to determine exact singlet product states is briefly discussed.
CRIS-Team WoS Importer:2020-05-02

Exact quantisation of U(1)3 quantum gravity via exponentiation of the hypersurface deformation algebroid - Thiemann, Thomas (Classical and Quantum Gravity, 2023)
The U(1)3 model for 3+1 Euclidian signature general relativity (GR) is an interacting, generally covariant field theory with two physical polarisations that shares many features of Lorentzian GR. In particular, it displays a non-trivial realisation of the hypersurface deformation algebroid with non-trivial, i.e. phase space dependent structure functions rather than structure constants. In this paper we show that the model admits an exact quantisation. The quantisation rests on the observation that for this model and in the chosen representation of the canonical commutation relations the density unity hypersurface algebra can be exponentiated on non-degenerate states. These are states that represent a non-degenerate quantum metric and from a classical perspective are the relevant states on which the hypersurface algebra is representable. The representation of the algebra is exact, with no ambiguities involved and anomaly free. The quantum constraints can be exactly solved using groupoid averaging and the solutions admit a Hilbert space structure that agrees with the quantisation of a recently found reduced phase space formulation. Using the also recently found covariant action for that model, we start a path integral or spin foam formulation which, due to the Abelian character of the gauge group, is much simpler than for Lorentzian signature GR and provides an ideal testing ground for general spin foam models. The solution of U(1)3 quantum gravity communicated in this paper motivates an entirely new approach to the implementation of the Hamiltonian constraint in quantum gravity.
CRIS-Team Scopus Importer:2023-12-01
Keywords: Bergmann Komar group; hypersurface deformation algebroid; quantum gravity

Excitations in one-dimensional S = 1/2 quantum antiferromagnets - Schmidt, Kai Phillip; et al. (Physical Review Letters, 2003)
The transition from dimerized to uniform phases is studied in terms of spectral weights for spin chains using continuous unitary transformations. The spectral weights in the S=1 channel are computed perturbatively around the limit of strong dimerization. We find that the spectral weight is concentrated mainly in the subspaces with a small number of elementary triplets (triplons), even for vanishing dimerization. So, besides spinons, triplons may be used as elementary excitations in spin chains. We conclude that there is no necessity to use fractional excitations in low-dimensional, undoped, or doped quantum antiferromagnets.

Excitonic magnetism at the intersection of spin-orbit coupling and crystal-field splitting - Feldmaier, Teresa; Strobel, Pascal; Schmid, Michael; Hansmann, Philipp; Daghofer, Maria (Physical Review Research, 2020)
Excitonic magnetism involving superpositions of singlet and triplet states is expected to arise for two holes in strongly correlated and spin-orbit-coupled t(2g) orbitals. However, uncontested material examples for its realization are rare. We apply the variational cluster approach to the square lattice to investigate excitonic antiferromagnetism and the impact of a crystal field. We give a phase diagram depending on spin-orbit coupling and crystal field and find excitonic magnetism to survive in the presence of substantial crystal-field-induced orbital order. We address the specific example of Ca2RuO4 using ab initio modeling and conclude it to realize such excitonic magnetism despite its pronounced orbital polarization. We also reproduce magnetic excitations and show the maximum at momentum (0,0) to be related to the excitonic character of the magnetic order.
CRIS-Team WoS Importer:2021-01-22

Existence of Replica-Symmetry Breaking in Quantum Glasses - Leschke, Hajo; Manai, Chokri; Ruder, Rainer; Warzel, Simone (Physical Review Letters, 2021)
By controlling quantum fluctuations via the Falk-Bruch inequality we give the first rigorous argument for the existence of a spin-glass phase in the quantum Sherrington-Kirkpatrick model with a "transverse"magnetic field if the temperature and the field are sufficiently low. The argument also applies to the generalization of the model with multispin interactions, sometimes dubbed as the transverse p-spin model.
CRIS-Team Scopus Importer:2021-11-26

Exotic cluster structures in the mean-field theory - Klatt, Michael; Ichikawa, T.; Iida, K.; Itagaki, N.; Maruhn, J. A.; Matsuyanagi, K.; Mecke, Klaus; Ohkubo, S.; Reinhard, Paul-Gerhard; Schuetrumpf, B. (Journal of Physics: Conference Series, 2013)
Investigations of exotic cluster-like phenomena in the framework of the Skyrme-Hartree-Fock approach are reported. The occurrence of highly excited isomeric states is discussed in connection with the question of their stability in static and time-dependent Hartree Fock (TDHF) calculations. We find rotational stabilization of a 4α chain structure in 16O occurring for a limited range of angular momenta. A toroidal configuration of 40Ca was also stabilized by rotation and provides a very interesting example of rotation about a symmetry axis with a strictly quantized total angular momentum. Finally we look at the formation of nuclear pasta phases in a time-dependent approach and their classification.
CRIS-Team Scopus Importer:2023-07-24

Exotic magnetization plateaus in a quasi-two-dimensional Shastry-Sutherland model - Foltin, G. R.; Manmana, S. R.; Schmidt, Kai Phillip (Physical Review B, 2014)
We find unconventional Mott insulators in a quasi-2D version of the Shastry-Sutherland model in a magnetic field. In our realization on a four-leg tube geometry, these are stabilized by correlated hopping of localized magnetic excitations. Using perturbative continuous unitary transformations (pCUTs, plus classical approximation or exact diagonalization) and the density matrix renormalisation group method (DMRG), we identify prominent magnetization plateaus at magnetizations M = 1/8, 3/16, 1/4, and 1/2. While the plateau at M = 1/4 can be understood in a semiclassical fashion in terms of diagonal stripes, the plateau at M = 1/8 displays highly entangled wheels in the transverse direction of the tube. Finally, the M = 3/16 plateau is most likely to be viewed as a classical 1/8 structure on which additional triplets are fully delocalized around the tube. The classical approximation of the effective model fails to describe all these plateau structures which benefit from correlated hopping. We relate our findings to the full 2D system, which is the underlying model for the frustrated quantum magnet SrCu(BO3)(2).

Expanding Nuclear Physics Horizons with the Gamma Factory - Budker, Dmitry; Berengut, Julian C.; Flambaum, Victor V.; Gorchtein, Mikhail; Jin, Junlan; Karbstein, Felix; Krasny, Mieczyslaw Witold; Litvinov, Yuri A.; Pálffy, Adriana; Pascalutsa, Vladimir; Petrenko, Alexey; Surzhykov, Andrey; et al. (Annalen Der Physik, 2022)
The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to approximate to 400 MeV and photon fluxes (up to approximate to 10(17) photons s(-1)) exceeding those of the currently available gamma sources by orders of magnitude. The high-energy (secondary) photons are produced via resonant scattering of the primary laser photons by highly relativistic partially-stripped ions circulating in the accelerator. The secondary photons are emitted in a narrow cone and the energy of the beam can be monochromatized, down to 10(-3)-10(-6) level, via collimation, at the expense of the photon flux. This paper surveys the new opportunities that may be afforded by the GF in nuclear physics and related fields.
CRIS-Team WoS Importer:2022-03-11

Expansion cone for the 3-inch PMTs of the KM3NeT optical modules - Adrian-Martinez, S.; Ageron, M.; Aguilar, J. A.; Aharonian, F.; Aiello, S.; Albert, A.; Alexandri, M.; Ameli, F.; Anassontzis, E. G.; Anghinolfi, M.; Anton, Gisela; Anvar, S.; et al. (Journal of Instrumentation, 2013)
Detection of high-energy neutrinos from distant astrophysical sources will open a new window on the Universe. The detection principle exploits the measurement of Cherenkov light emitted by charged particles resulting from neutrino interactions in the matter containing the telescope. A novel multi-PMT digital optical module (DOM) was developed to contain 31 3-inch photomultiplier tubes (PMTs). In order to maximize the detector sensitivity, each PMT will be surrounded by an expansion cone which collects photons that would otherwise miss the photocathode. Results for various angles of incidence with respect to the PMT surface indicate an increase in collection efficiency by 30% on average for angles up to 45 degrees with respect to the perpendicular. Ray-tracing calculations could reproduce the measurements, allowing to estimate an increase in the overall photocathode sensitivity, integrated over all angles of incidence, by 27% (for a single PMT). Prototype DOMs, being built by the KM3NeT consortium, will be equipped with these expansion cones.
Keywords: Optical detector readout concepts; Instrument optimisation; Cherenkov detectors; Large detector systems for particle and astroparticle physics

Expectation values of coherent states for SU(2) Lattice Gauge Theories - Liegener, Klaus; Zwicknagel, Ernst-Albrecht (Journal of High Energy Physics, 2020)
This article investigates properties of semiclassical Gauge Field Theory Coherent States for general quantum gauge theories. Useful, e.g., for the canonical formulation of Lattice Gauge Theories these states are labelled by a point in the classical phase space and constructed such that the expectation values of the canonical operators are sharply peaked on said phase space point. For the case of the non-abelian gauge group SU(2), we will explicitly compute the expectation value of general polynomials including the first order quantum corrections. This allows asking more precise questions about the quantum fluctuations of any given semiclassical system.
CRIS-Team Scopus Importer:2020-02-18
Keywords: Beyond Standard Model; Gauge Symmetry; Lattice Quantum Field Theory; Nonperturbative Effects

Expectation Values of Holonomy-Operators in Cosmological Coherent States for Loop Quantum Gravity - Zwicknagel, Ernst-Albrecht; Giesel, Kristina; Liegener, Klaus (2018)

Experimental Evidence for Quantum Interference and Vibrationally Induced Decoherence in Single-Molecule Junctions - Ballmann, Stefan; Härtle, Rainer; Brana Coto, Pedro; Elbing, Mark; Mayor, Marcel; Bryce, Martin; Thoss, Michael; Weber, Heiko B. (Physical Review Letters, 2012)
We analyze quantum interference and decoherence effects in single-molecule junctions both experimentally and theoretically by means of the mechanically controlled break junction technique and density-functional theory. We consider the case where interference is provided by overlapping quasidegenerate states. Decoherence mechanisms arising from electronic-vibrational coupling strongly affect the electrical current flowing through a single-molecule contact and can be controlled by temperature variation. Our findings underline the universal relevance of vibrations for understanding charge transport through molecular junctions. © 2012 American Physical Society.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.LAP.experi

Experimental simulation of loop quantum gravity on a photonic chip - Van Der Meer, Reinier; Huang, Zichang; Anguita, Malaquias Correa; Qu, Dongxue; Hooijschuur, Peter; Liu, Hongguang; Han, Muxin; Renema, Jelmer J.; Cohen, Lior (npj Quantum Information, 2023)
The unification of general relativity and quantum theory is one of the fascinating problems of modern physics. One leading solution is Loop Quantum Gravity (LQG). Simulating LQG may be important for providing predictions which can then be tested experimentally. However, such complex quantum simulations cannot run efficiently on classical computers, and quantum computers or simulators are needed. Here, we experimentally demonstrate quantum simulations of spinfoam amplitudes of LQG on an integrated photonics quantum processor. We simulate a basic transition of LQG and show that the derived spinfoam vertex amplitude falls within 4% error with respect to the theoretical prediction, despite experimental imperfections. We also discuss how to generalize the simulation for more complex transitions, in realistic experimental conditions, which will eventually lead to a quantum advantage demonstration as well as expand the toolbox to investigate LQG.
CRIS-Team Scopus Importer:2023-04-28

Exploration of a modified density dependence in the skyrme functional - Erler, J.; Klüpfe, P.; Reinhard, Paul-Gerhard (Physical Review C - Nuclear Physics, 2010)
A variant of the basic Skyrme-Hartree-Fock functional is considered dealing with a new form of density dependence. It employs only integer powers and thus will allow a more sound basis for projection schemes (particle number, angular momentum).We optimize the new functional with exactly the same adjustment strategy as used in an earlier study with a standard Skyrme functional. This allows direct comparisons of the performance of the new functional relative to the standard one.We discuss various observables: bulk properties of finite nuclei, nuclear matter, giant resonances, superheavy elements, and energy systematics. The new functional performs at least as well as the standard one, but offers a wider range of applicability (e.g., for projection) and more flexibility in the regime of high densities. © 2010 The American Physical Society.
CRIS-Team Scopus Importer:2023-07-24

Exploring Reactive Conformations of Coenzyme A during Binding and Unbinding to Pyruvate Formate-Lyase - Hanzevacki, Marko; Banhatti, Radha Dilip; Čondić-Jurkić, Karmen; Smith, Ana-Suncana; Smith, David M. (Journal of Physical Chemistry A, 2019)
Pyruvate formate-lyase (PFL) is a glycyl radical enzyme that converts pyruvate and coenzyme A (CoA) into formate and acetyl-CoA in two half-reactions. Recently, we showed that the acetylation of the PFL active site in the first half-reaction induces subtle conformational changes, leading to the opening of a potential channel for CoA entry. Entry of CoA into the active site is crucial for the second half-reaction, involving the acetyl transfer to CoA, and the completion of the catalytic cycle. Using steered molecular dynamics (SMD) simulations, performed on acetylated and nonacetylated monomeric PFL model systems, we first of all investigate the possible entry/exit pathways of CoA with respect to the active site through the previously identified channel. We then perform umbrella sampling simulations on multiple snapshots from SMD trajectories as well as unrestrained molecular dynamics simulations starting from the final structures obtained from entry SMD, with a view to identifying possible bound states of CoA in the near vicinity of the active site. Detailed study of the unrestrained dissociation processes reveals the presence of stable and reactive bound states of CoA close to the active site, one of which is in an ideal position for triggering the second half-reaction. Examination of the spatial distributions associated with the reactive bound states allows us to discuss the free energy barriers. Umbrella sampling, performed on snapshots from unrestrained dynamics confirms the above findings. The significance of the results for the catalysis are discussed for both acetylated and nonacetylated systems.
CRIS-Team Scopus Importer:2019-11-01

Exploring small energy scales with x-ray absorption and dichroism - Praetorius, C.; Zinner, M.; Hansmann, Philipp; Haverkort, M. W.; Fauth, Kai (Physical Review B, 2016)
Soft x-ray linear and circular dichroism (XLD, XMCD) experiments at the Ce M-4,M-5 edges are being used to determine the energy scales characterizing the Ce 4f degrees of freedom in the ultrathin ordered surface intermetallic CeAgx/Ag(111). We find that all relevant interactions, i.e., Kondo scattering, crystal field splitting and magnetic exchange coupling occur on small scales. Our study demonstrates the usefulness of combining x-ray absorption experiments probing the temperature dependence of both linear and circular dichroism owing to their strong sensitivity for anisotropies in both charge distribution and paramagnetic response, respectively.
CRIS-Team WoS Importer:2020-02-19

Exploring the diffeomorphism-invariant Hilbert space of a scalar field - Sahlmann, Hanno (Classical and Quantum Gravity, 2007)
As a toy model for the implementation of the diffeomorphism constraint, the interpretation of the resulting states and the treatment of ordering ambiguities in loop quantum gravity, we consider the Hilbert space of spatially diffeomorphism-invariant states for a scalar field. We give a very explicit formula for the scalar product on this space and discuss its structure. Then we turn to the quantization of a certain class of diffeomorphism-invariant quantities on that space and discuss in detail the ordering issues involved. On a technical level these issues bear some similarity to those encountered in full loop quantum gravity. © 2007 IOP Publishing Ltd.

Exploring the diffeomorphism invariant Hilbert space of a scalar field - Sahlmann, Hanno (11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories, MG 2006, 2008)
As a toy model for the implementation of the diffeomorphism constraint, the interpretation of the resulting states, and the treatment of ordering ambiguities in loop quantum gravity, we consider the Hilbert space of spatially diffeomorphism invariant states for a scalar field. We give a very explicit formula for the scalar product on this space, and discuss its structure. Then we turn to the quantization of a certain class of diffeomorphism invariant quantities on that space, and discuss in detail the ordering issues involved. © 2008 World Scientific Publishing Co. Pte. Ltd.

Extensions of the Duflo map and Chern-Simons expectation values - Sahlmann, Hanno; Zilker, Thomas (Journal of Geometry and Physics, 2017)
The Duflo map is a valuable tool for operator ordering in contexts in which Kirillov-Kostant brackets and their quantizations play a role. A priori, the Duflo map is only defined on the subspace of the symmetric algebra over a Lie algebra consisting of elements invariant under the adjoint action. Here we discuss extensions to the whole symmetric algebra, as well as their application to the calculation of Chern-Simons theory expectation values.

Extracting critical exponents for sequences of numerical data via series extrapolation techniques - Coester, Kris; Schmidt, Kai Phillip (Physical Review E, 2016)
We describe a generic scheme to extract critical exponents of quantum lattice models from sequences of numerical data, which is, for example, relevant for nonperturbative linked-cluster expansions or nonperturbative variants of continuous unitary transformations. The fundamental idea behind our approach is a reformulation of the numerical data sequences as a series expansion in a pseudoparameter. This allows us to utilize standard series expansion extrapolation techniques to extract critical properties such as critical points and critical exponents. The approach is illustrated for the deconfinement transition of the antiferromagnetic spin-1/2 Heisenberg chain.

Fabrication and characterization of three-dimensional biomimetic chiral composites - Turner, Mark D.; Schröder-Turk, Gerd; Gu, Min (Optics Express, 2011)
Here we show the fabrication and characterization of a novel class of biomimetic photonic chiral composites inspired by a recent finding in butterfly wing-scales. These three-dimensional networks have cubic symmetry, are fully interconnected, have robust mechanical strength and possess chirality which can be controlled through the composition of multiple chiral networks, providing an excellent platform for developing novel chiral materials. Using direct laser writing we have fabricated different types of chiral composites that can be engineered to form novel photonic devices. We experimentally show strong circular dichroism and compare with numerical simulations to illustrate the high quality of these three-dimensional photonic structures.
EAM Import::2019-03-14

Facile colloidal coating of polystyrene nanospheres with tunable gold dendritic patches - Bao, Huixin; Bihr, Timo; Smith, Ana-Suncana; Klupp Taylor, Robin (Nanoscale, 2014)
Patchy particles comprise regions of differing material or chemical functionality on otherwise isotropic cores. To meet the great potential of these anisotropic structures in a wide range of application fields, completely new approaches are sought for the scalable and tunable production of patchy particles, particularly those with nanoscale dimensions. In this paper the synthesis of patchy particles via a simple colloidal route is investigated. Using surfactant-free cationic polystyrene nanospheres as core particles, gold patches are produced through the in situ reduction of chloroauric acid with ascorbic acid. The fact that such nanostructured metal patches can be heterogeneously nucleated on polymer nanospheres is related to the electrostatic interaction between core and metal precursor. Furthermore, the lateral expansion of the gold patches over the polystyrene surface is facilitated by an excess of ascorbic acid. The morphology of the patches is highly dendritic and process-induced variations in the structure are related to gold surface mobility using Monte Carlo simulations based on the diffusion limited aggregation principle. Considering the pH dependent behaviour of ascorbic acid it is possible to predict the moiety which most likely adsorbs to the polymer surface and promotes gold surface diffusion. This enables the judicious adjustment of the pH to also obtain non-dendritic patches. On account of the plasmonic behaviour of gold, the patchy particles have morphology-dependent optical properties. The systematic development of the synthetic approach described here is expected to lay a foundation for the development of functional materials based on the self- or directed-assembly of nanoscale building blocks with anisotropic interactions and properties. © the Partner Organisations 2014.
Keywords: patchy; particle; functionality; anisotropic; morphology; Monte-Carlo; simulation; surface

Family of Exactly Solvable Models with an Ultimate Quantum Paramagnetic Ground State - Schmidt, Kai Phillip; Laad, Mukul (Physical Review Letters, 2010)
We present a family of two-dimensional frustrated quantum magnets solely based on pure nearest-neighbor Heisenberg interactions which can be solved quasiexactly. All lattices are constructed in terms of frustrated quantum cages containing a chiral degree of freedom protected by frustration. The ground states of these models are dubbed ultimate quantum paramagnets and exhibit an extensive entropy at zero temperature. We discuss the unusual and extensively degenerate excitations in such phases. Implications for thermodynamic properties as well as for decoherence free quantum computation are discussed.

Far from the equilibrium crowd - Schmiedeberg, Michael (Nature Physics, 2023)

Fate of Dirac points in a vortex superlattice - Kamfor, Michael; Dusuel, Sebastien; Schmidt, Kai Phillip; Vidal, Julien (Physical Review B, 2011)
We consider noninteracting fermions on the honeycomb lattice in the presence of a magnetic vortex superlattice. It is shown that depending on the superlattice periodicity, a gap may open at zero energy. We derive an expression of the gap in the small-flux limit but the main qualitative features are found to be valid for arbitrary fluxes. This study provides an original example of a metal-insulator transition induced by a strongly modulated magnetic field in graphene. At the same time, our results directly apply to Kitaev's honeycomb model in a vortex superlattice.

Fate of orbitons coupled to phonons - Schmidt, Kai Phillip; et al. (Physical Review B, 2007)
The key feature of an orbital wave or orbiton is a significant dispersion, which arises from exchange interactions between orbitals on distinct sites. We study the effect of a coupling between orbitons and phonons in one dimension using continuous unitary transformations. Already for intermediate values of the coupling, the orbiton band width is strongly reduced and the spectral density is dominated by an orbiton-phonon continuum. However, we find sharp features within the continuum and an orbiton-phonon antibound state above. Both show a significant dispersion and should be observable experimentally.

Fate of the cluster state on the square lattice in a magnetic field - Kalis, Henning; Klagges, Daniel; Orus, Roman; Schmidt, Kai Phillip (Physical Review A, 2012)
The cluster state represents a highly entangled state which is one central object for measurement-based quantum computing. Here we study the robustness of the cluster state on the two-dimensional square lattice at zero temperature in the presence of external magnetic fields by means of different types of high-order series expansions and variational techniques using infinite projected entangled pair states. The phase diagram displays a first-order phase transition line ending in two critical end points. Furthermore, it contains a characteristic self-dual line in parameter space allowing many precise statements. The self-duality is shown to exist on any lattice topology.

Fermion spins in loop quantum gravity - Mansuroglu, Refik; Sahlmann, Hanno (Physical Review D, 2021)
We define and study kinematical observables involving fermion spin, such as the total spin of a collection of particles, in loop quantum gravity. Due to the requirement of gauge invariance, the relevant quantum states contain strong entanglement between gravity and fermionic degrees of freedom. Interestingly we fmd that properties and spectra of the observables are nevertheless similar to their counterparts from quantum mechanics. However, there are also new effects. Due to the entanglement between gravity and fermionic degrees of freedom, alignment of quantum spins has consequences for quantized geometry. We sketch a particular effect of this kind that may in principle be observable.
CRIS-Team WoS Importer:2021-06-04

Fiber Network Elasticity as Function of Crosslinker Density - Sporer, Susan; Kapfer, Sebastian; Arns, Christoph; Mecke, Klaus; Schröder-Turk, Gerd (Biophysical Journal, 2010)

Field induced spontaneous quasiparticle decay and renormalization of quasiparticle dispersion in a quantum antiferromagnet - Hong, Tao; Qiu, Y.; Matsumoto, M.; Tennant, D. A.; Coester, K.; Schmidt, Kai Phillip; Awwadi, F. F.; Turnbull, M. M.; Agrawal, H.; Chernyshev, A. L. (Nature Communications, 2017)
The notion of a quasiparticle, such as a phonon, a roton or a magnon, is used in modern condensed matter physics to describe an elementary collective excitation. The intrinsic zero-temperature magnon damping in quantum spin systems can be driven by the interaction of the one-magnon states and multi-magnon continuum. However, detailed experimental studies on this quantum many-body effect induced by an applied magnetic field are rare. Here we present a high-resolution neutron scattering study in high fields on an S = 1/2 antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear spin-wave theory, our results demonstrate a variety of phenomena including field-induced renormalization of one-magnon dispersion, spontaneous magnon decay observed via intrinsic linewidth broadening, unusual non-Lorentzian two-peak structure in the excitation spectra and a dramatic shift of spectral weight from one-magnon state to the two-magnon continuum.

Field-Induced Tomonaga-Luttinger Liquid Phase of a Two-Leg Spin-1/2 Ladder with Strong Leg Interactions - Hong, Tao; Kim, Y. H.; Hotta, C.; Takano, Y.; Tremelling, G.; Turnbull, M. M.; Landee, C. P.; Kang, H. -J.; Christensen, N. B.; Lefmann, Kim; Schmidt, Kai Phillip; Uhrig, G. S.; et al. (Physical Review Letters, 2010)
We study the magnetic-field-induced quantum phase transition from a gapped quantum phase that has no magnetic long-range order into a gapless phase in the spin-1/2 ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY). At temperatures below about 1 K, the specific heat in the gapless phase attains an asymptotic linear temperature dependence, characteristic of a Tomonaga-Luttinger liquid. Inelastic neutron scattering and the specific heat measurements in both phases are in good agreement with theoretical calculations, demonstrating that DIMPY is the first model material for an S = 1/2 two-leg spin ladder in the strong-leg regime.

Fiktionen, Simulationen, Dialoge. Erkenntnisstrategien in Wissenschaft, Erzählung und Philosophie. Michael Hampe im Dialog zu »Tunguska oder Das Ende der Natur« - Heydenreich, Aura; Mecke, Klaus (Physik und Poetik. Produktionsästhetik und Werkgenese. Autorinnen und Autoren im Dialog, 2015)

Finding Auxetic Frameworks in Periodic Tessellations - Mitschke, Holger; Schwerdtfeger, Jan; Schury, Fabian; Stingl, Michael; Körner, Carolin; Singer, Robert; Robins, Vanessa; Mecke, Klaus; Schröder-Turk, Gerd (Advanced Materials, 2011)
It appears that most models for micro-structured materials with auxetic deformations were found by clever intuition, possibly combined with optimization tools, rather than by systematic searches of existing structure archives. Here we review our recent approach of finding micro-structured materials with auxetic mechanisms within the vast repositories of planar tessellations. This approach has produced two previously unknown auxetic mechanisms, which have Poisson's ratio v(ss) = -1 when realized as a skeletal structure of stiff incompressible struts pivoting freely at common vertices. One of these, baptized Triangle-Square Wheels, has been produced as a linear-elastic cellular structure from Ti-6Al-4V alloy by selective electron beam melting. Its linear-elastic properties were measured by tensile experiments and yield an effective Poisson's ratio v(LE) approximate to -0.75, also in agreement with finite element modeling. The similarity between the Poisson's ratios v(SS) of the skeletal structure and v(LE) of the linear-elastic cellular structure emphasizes the fundamental role of geometry for deformation behavior, regardless of the mechanical details of the system. The approach of exploiting structure archives as candidate geometries for auxetic materials also applies to spatial networks and tessellations and can aid the quest for inherently three-dimensional auxetic mechanisms.

Fine Grained Tensor Network Methods - Schmoll, Philipp; Jahromi, Saeed S.; Hörmann, Max; Schmidt, Kai Phillip; Orus, Roman (Physical Review Letters, 2020)
We develop a strategy for tensor network algorithms that allows to deal very efficiently with lattices of high connectivity. The basic idea is to fine grain the physical degrees of freedom, i.e., decompose them into more fundamental units which, after a suitable coarse graining, provide the original ones. Thanks to this procedure, the original lattice with high connectivity is transformed by an isometry into a simpler structure, which is easier to simulate via usual tensor network methods. In particular this enables the use of standard schemes to contract infinite 2D tensor networks-such as corner transfer matrix renormalization schemes-which are more involved on complex lattice structures. We prove the validity of our approach by numerically computing the ground-state properties of the ferromagnetic spin-1 transverse-field Ising model on the 2D triangular and 3D stacked triangular lattice, as well as of the hardcore and softcore Bose-Hubbard models on the triangular lattice. Our results are benchmarked against those obtained with other techniques, such as perturbative continuous unitary transformations and graph projected entangled pair states, showing excellent agreement and also improved performance in several regimes.
CRIS-Team WoS Importer:2020-06-02

Finite auxetic deformations of plane tessellations - Mitschke, Holger; Robins, Vanessa; Mecke, Klaus; Schröder-Turk, Gerd (Proceedings of the Royal Society A-Mathematical Physical and Engineering Sciences, 2013)
We systematically analyse the mechanical deformation behaviour, in particular Poisson's ratio, of floppy bar-and-joint frameworks based on periodic tessellations of the plane. For frameworks with more than one deformation mode, crystallographic symmetry constraints or minimization of an angular vertex energy functional are used to lift this ambiguity. Our analysis allows for systematic searches for auxetic mechanisms in archives of tessellations; applied to the class of one- or two-uniform tessellations by regular or star polygons, we find two auxetic structures of hexagonal symmetry and demonstrate that several other tessellations become auxetic when retaining symmetries during the deformation, in some cases with large negative Poisson ratios nu < -1 for a specific lattice direction. We often find a transition to negative Poisson ratios at finite deformations for several tessellations, even if the undeformed tessellation is infinitesimally non-auxetic. Our numerical scheme is based on a solution of the quadratic equations enforcing constant edge lengths by a Newton method, with periodicity enforced by boundary conditions.
Keywords: Poisson's ratio; strain amplification; tilings and tessellations; isostaticity; skeletal frameworks; cellular structures

Finiteness of spinfoam vertex amplitude with timelike polyhedra and the regularization of full amplitude - Han, Muxin; Kaminski, Wojciech; Liu, Hongguang (Physical Review D, 2022)
This work focuses on Conrady-Hnybida's four-dimensional extended spinfoam model with timelike polyhedra, while we restrict all faces to be spacelike. First, we prove the absolute convergence of the vertex amplitude with timelike polyhedra, when SU(1, 1) boundary states are coherent states or the canonical basis, or their finite linear combinations. Second, based on the finite vertex amplitude and a proper prescription of the SU(1, 1) intertwiner space, we construct the extended spinfoam amplitude on an arbitrary cellular complex, taking into account the sum over SU(1, 1) intertwiners of internal timelike polyhedra. We observe that the sum over SU(1, 1) intertwiners is infinite for the internal timelike polyhedron that has at least two future-pointing and two past-pointing face normals. In order to regularize the possible divergence from summing over SU(1, 1) intertwiners, we develop a quantum cutoff scheme based on the eigenvalue of the "shadow operator". The spinfoam amplitude with timelike internal polyhedra (and spacelike faces) is finite, when two types of cutoffs are imposed. One is imposed on j the eigenvalue of area operator, and the other is imposed on the eigenvalue of the shadow operator for every internal timelike polyhedron that has at least two future-pointing and two past-pointing face normals.
CRIS-Team WoS Importer:2022-07-15

First-Principle Coarse-Graining Framework for Scale-Free Bell-Like Association and Dissociation Rates in Thermal and Active Systems - Janeš, Josip Augustin; Monzel, Cornelia; Schmidt, Daniel; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Physical Review X, 2022)
Fluctuations of surfaces that harbor reactive molecules interacting across the intervening space strongly influence the reaction kinetics. One such paradigmatic system is the cell membrane, with associated proteins, binding to an interior or an exterior scaffold - for example, the cytoskeleton in the former and the extracellular matrix in the latter case. Given that membrane fluctuations are significant and regulated by the activity of the cell, we hypothesize that these active fluctuations can be tuned to influence ligand-receptor-mediated adhesion. However, a comprehensive model, deriving both binding and unbinding rates from first principles, has not yet been established, and as such, the effect of the membrane activity on the rates remains an open problem. Here, we solve this issue by establishing a systematic coarse graining procedure, providing a cascade of expressions for rates appropriate for the observed timescale, and present a scale-free formulation of rates. In the first step, we introduce a minimal model to recover the so-called Bell-Dembo rates from first principles, where the binding and unbinding rates depend on the instantaneous position of the membrane. We then derive the analytical coarse-grained rates for thermal fluctuations, recovering a result that has previously been successfully used in the literature. Finally, we expand this framework to account for active fluctuations of the membrane. In this step, we develop a mechanical model that convolutes Gauss and Laplace distributed noise. This choice may have universal features and is motivated by our analysis of measurements in two very different cell types, namely, human macrophages and red blood cells. We find that cell activation enables the formation of bonds at much larger separations between the cell and the target. This effect is significantly greater for binding to a surface on the extracellular compared to the intracellular side. We thus show that active fluctuations directly influence protein association and dissociation rates, which may have clear physiological implications that are yet to be explored.
CRIS-Team Scopus Importer:2022-09-16

First results on dark matter annihilation in the Sun using the ANTARES neutrino telescope - Adrian-Martinez, S.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anton, L.; Anvar, S.; Ardid, Miguel; Astraatmadja, T.; Aubert, J-J.; Baret, B.; et al. (Journal of Cosmology and Astroparticle Physics, 2013)
A search for high-energy neutrinos coming from the direction of the Sun has been performed using the data recorded by the ANTARES neutrino telescope during 2007 and 2008. The neutrino selection criteria have been chosen to maximize the selection of possible signals produced by the self-annihilation of weakly interacting massive particles accumulated in the centre of the Sun with respect to the atmospheric background. After data unblinding, the number of neutrinos observed towards the Sun was found to be compatible with background expectations. The 90% CL upper limits in terms of spin-dependent and spin-independent WIMP-proton cross-sections are derived and compared to predictions of two supersymmetric models, CMSSM and MSSM-7. The ANTARES limits are comparable with those obtained by other neutrino observatories and are more stringent than those obtained by direct search experiments for the spin-dependent WIMP-proton cross-section in the case of hard self-annihilation channels (W+W-, tau(+)tau(-)).
Keywords: neutrino experiments; dark matter detectors; supersymmetry and cosmology; particle physics - cosmology connection

First search for neutrinos in correlation with gamma-ray bursts with the ANTARES neutrino telescope - 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. (Journal of Cosmology and Astroparticle Physics, 2013)
A search for neutrino-induced muons in correlation with a selection of 40 gamma-ray bursts that occurred in 2007 has been performed with the ANTARES neutrino telescope. During that period, the detector consisted of 5 detection lines. The ANTARES neutrino telescope is sensitive to TeV-PeV neutrinos that are predicted from gamma-ray bursts. No events were found in correlation with the prompt photon emission of the gamma-ray bursts and upper limits have been placed on the flux and fluence of neutrinos for different models.
Keywords: neutrino experiments; neutrino astronomy; gamma ray bursts theory

FIRST SEARCH FOR POINT SOURCES OF HIGH-ENERGY COSMIC NEUTRINOS WITH THE ANTARES NEUTRINO TELESCOPE - Adrian-Martinez, S.; Aguilar, J. A.; Al Samarai, I.; Albert, A.; Andre, Michel; Anghinolfi, M.; Anton, Gisela; Anvar, S.; Ardid, Miguel; Jesus, A. C. Assis; Astraatmadja, T.; Aubert, J. -J.; et al. (Astrophysical Journal Letters, 2011)
Results are presented of a search for cosmic sources of high-energy neutrinos with the ANTARES neutrino telescope. The data were collected during 2007 and 2008 using detector configurations containing between 5 and 12 detection lines. The integrated live time of the analyzed data is 304 days. Muon tracks are reconstructed using a likelihood-based algorithm. Studies of the detector timing indicate a median angular resolution of 0.5 +/- 0.1 deg. The neutrino flux sensitivity is 7.5 x 10(-8)(E(v)/GeV)(-2) GeV(-1) s(-1) cm(-2) for the part of the sky that is always visible (delta < -48 deg), which is better than limits obtained by previous experiments. No cosmic neutrino sources have been observed.
Keywords: astroparticle physics; cosmic rays; neutrinos

Fission of super-heavy nuclei explored with skyrme forces - Schindzielorz, Nils; Erler, J.; Klüpfel, P.; Reinhard, Paul-Gerhard; Hager, Georg (International Journal of Modern Physics E-Nuclear Physics, 2009)
We present a large scale survey of life-times for spontaneous fission in the regime of super-heavy elements (SHE), i.e. nuclei with Z=104-122. This is done on the basis of the Skyrme-Hartree-Fock model. The axially symmetric fission path is computed using a quadrupole constraint. Self-consistent cranking is used for the collective masses and associated quantum corrections. The actual tunneling probability is estimated by the WKB approximation. Three typical Skyrme forces are used to explore the sensitivity of the results. Benchmarks in the regime Z=104-108 show an acceptable agreement. The general systematics reflects nicely the islands of shell stabilization and the crossover from α-decay to fission for the decay chains from the region of Z/N=118/176. © 2009 World Scientific Publishing Company.
CRIS-Team Scopus Importer:2023-07-24

Fission properties for r-process nuclei - Erler, J.; Langanke, K.; Loens, H. P.; Martínez-Pinedo, G.; Reinhard, Paul-Gerhard (Physical Review C - Nuclear Physics, 2012)
We present a systematics of fission barriers and fission lifetimes for the whole landscape of superheavy elements (SHE), i.e., nuclei with Z100. The fission lifetimes are also compared with the α-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parametrizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. The computation of fission lifetimes takes care of the crucial ingredients of the large-amplitude collective dynamics along the fission path, as self-consistent collective mass and proper quantum corrections. We discuss the different topologies of fission landscapes which occur in the realm of SHE (symmetric versus asymmetric fission, regions of triaxial fission, bimodal fission, and the impact of asymmetric ground states). The explored region is extended deep into the regime of very neutron-rich isotopes as they are expected to be produced in the astrophysical r process. © 2012 American Physical Society.
CRIS-Team Scopus Importer:2023-07-24

Floquet engineering of molecular dynamics via infrared coupling - Reitz, Michael; Genes, Claudiu (Journal of Chemical Physics, 2020)
We discuss Floquet engineering of dissipative molecular systems through periodic driving of an infrared-active vibrational transition, either directly or via a cavity mode. Following a polaron quantum Langevin equation approach, we derive correlation functions and stationary quantities showing strongly modified optical response of the infrared-dressed molecule. The coherent excitation of molecular vibrational modes in combination with the modulation of electronic degrees of freedom due to vibronic coupling can lead to both enhanced vibronic coherence and control over vibrational sideband amplitudes. The additional coupling to an infrared cavity allows for the controlled suppression of undesired sidebands, an effect stemming from the Purcell enhancement of vibrational relaxation rates.
CRIS-Team WoS Importer:2021-01-22

Fluctuating lipid bilayer in an arbitrary potential: Theory and experimental determination of bending rigidity - Mecke, Klaus; et al. (Langmuir, 2003)
We consider the position fluctuations of a membrane close to a substrate in an external potential and at finite temperature. We derive self-consistent equations for the average membrane position and its root mean square fluctuation amplitude in the range of moderate fluctuations much below the unbinding transition. These self-consistent equations can be solved for arbitrary potentials. We first check them for special known cases, then we apply our approach to lipid bilayers where van der Waals attractions are balanced by hydration repulsion associated to a hard wall. Finally, we compare these results with recent experiments on lipid bilayer.(1).

Fluctuation control of nonthermal orbital order - Grandi, Francesco; Eckstein, Martin (Physical Review B, 2021)
Orbitally ordered states exhibit unique features which make them a promising platform for exploring the ultrafast dynamics of long-range order in solids: Their free energy typically has multiple discrete minima, and electric laser fields or selectively excited phonons can exert effective forces that may be used to steer the order parameter through these free-energy landscapes. Moreover, their free energy strongly depends on fluctuations, and in some cases restoring forces close to a minimum are exclusively of entropic origin (order-by-disorder mechanisms). This can open pathways to control the dynamics of the order parameter via nonthermal fluctuations. In this paper, we study the laser-induced nonequilibrium dynamics in a 120 compass model, using time-dependent Ginzburg-Landau theory. We analyze protocols to switch the order parameter between equivalent configurations, with a focus on the interplay between the external force due to the driving field and the nonthermal entropic forces. In particular, we find that remanent nonthermal fluctuations after some excitation can stabilize the high-symmetry phase even when the homogeneous potential has retrieved its low-temperature form, which facilitates laser-induced switching.
CRIS-Team Scopus Importer:2021-07-02

Fluids in Extreme Confinement - Franosch, Thomas; Lang, Simon; Schilling, Rolf (Physical Review Letters, 2012)
For extremely confined fluids with a two-dimensional density n in slit geometry of an accessible width L, we prove that in the limit Li̊ghtarrow0, the lateral and transversal degrees of freedom decouple, and the latter become ideal-gas-like. For a small wall separation, the transverse degrees of freedom can be integrated out and renormalize the interaction potential. We identify nL2 as the hidden smallness parameter of the confinement problem and evaluate the effective two-body potential analytically, which allows calculating the leading correction to the free energy exactly. Explicitly, we map a fluid of hard spheres in extreme confinement onto a 2D fluid of disks with an effective hard-core diameter and a soft boundary layer. Two-dimensional phase transitions are robust and the transition point experiences a shift O(nL2).
EAM Import::2019-03-14

Fluids in porous media: a morphometric approach - Mecke, Klaus; et al. (2005)
Also the thermodynamic behaviour of fluids in porous media, i.e., the shape dependence of the grand canonical potential and of surface energies of a fluid bounded by an arbitrarily shaped convex pore, can be calculated in the thermodynamic limit fully from the knowledge of the Minkowski functionals, i.e., of only four morphometric measures. This remarkable result is based on Hadwiger's theorem on the completeness of the additive Minkowski functionals and the assumption that a thermodynamic potential is an 'additive' functional which can be understood as a more precise definition for the conventional term 'extensive'. As a consequence, the surface energy and other thermodynamic quantities contain in the thermodynamic limit, beside a constant term, only contributions linear in the mean and Gaussian curvature of the pore and not an infinite number of curvature terms. Finally, starting from a microscopic density functional for an inhomogeneous fluid in a porous medium the phase coexistence (capillary condensation) and the critical point of the fluid is determined in terms of structure functions and morphological measures of the pore space and calculated explicitly for specific random porous structures using results from integral geometry.

Fock quantization of the Dirac field in hybrid quantum cosmology: Relation with adiabatic states - Elizaga de Navascués, Beatriz; Mena Marugan, Guillermo A.; Prado, Santiago (Physical Review D, 2019)
We study the relation between the Fock representations for a Dirac field given by the adiabatic scheme and the unique family of vacua with a unitarily implementable quantum evolution that is employed in hybrid quantum cosmology. This is done in the context of a perturbed flat cosmology that, in addition, is minimally coupled to fermionic perturbations. In our description, we use a canonical formulation for the entire system, formed by the underlying cosmological spacetime and all its perturbations. After introducing an adiabatic scheme that was originally developed in the context of quantum field theory in fixed cosmological backgrounds, we find that all adiabatic states belong to the family of Fock representations that allow a unitarily implementable quantum evolution (although the converse is not generally true). In particular, this unitarity of the dynamics ensures that the vacua defined with adiabatic initial conditions at different times are unitarily equivalent. We also find that, for all adiabatic orders other than 0, these initial conditions allow the definition of annihilation and creation operators for the Dirac field that lead to some finite backreaction in the quantum Hamiltonian constraint and to a fermionic Hamiltonian operator that is properly defined in the span of the n-particle/antiparticle states, in the context of hybrid quantum cosmology.
CRIS-Team WoS Importer:2019-12-20

Forbidden subspaces for level-1 quantum approximate optimization algorithm and instantaneous quantum polynomial circuits - Streif, Michael; Leib, Martin (Physical Review A, 2020)
We present a thorough investigation of problems that can be solved exactly with the level-1 quantum approximate optimization algorithm (QAOA). To this end, we implicitly define a class of problem Hamiltonians that are employed as phase separators in a level-1 QAOA circuit and provide unit overlap with a target subspace spanned by a set of computational basis states. For one-dimensional target subspaces, we identify instances within the implicitly defined class of Hamiltonians for which quantum annealing (QA) and simulated annealing (SA) have an exponentially small probability of finding the solution. Consequently, our results define a demarcation line between QAOA on one hand and QA and SA on the other, and highlight the fundamental differences between an interference-based search heuristic such as QAOA and heuristics that are based on thermal and quantum fluctuations like SA and QA respectively. Moreover, for two-dimensional solution subspaces, we are able to show that the depth of the QAOA circuit grows linearly with the Hamming distance between the two target states. We further show that there are no genuine solutions for target subspaces of dimension higher than 2 and smaller than 2n. We also transfer these results to instantaneous quantum polynomial (IQP) circuits.
CRIS-Team Scopus Importer:2020-11-13

Force-induced de-adhesion of specifically bound vesicles: Strong adhesion in competition with tether extraction - Smith, Ana-Suncana; Seifert, Udo (Langmuir, 2005)
A theoretical study of the thermodynamic equilibrium between force-induced tether formation and the adhesion of vesicles mediated by specific ligand-receptor interactions has been performed. The formation of bonds between mobile ligands in the vesicle and immobile receptors on the substrate is examined within a thermodynamic approximation. The shape of a vesicle pulled with a point force is calculated within a continuous approach. The two approaches are merged self-consistently by the use of the effective adhesion potential produced by the collective action of the bonds. As a result, the shapes of the vesicle and the tether, as well as the number of formed bonds in the contact zone, are determined as a function of the force, and approximate analytic expressions for them are provided. The de-adhesion process is characterized by the construction of a phase diagram that is a function of the density of the ligands in the vesicle, the surface coverage by receptors, the ligand-receptor binding affinity, and the reduced volume of the vesicle. In all cases, the phase diagram contains three regions separated by two nonintersecting lines of critical forces. The first is the line of onset forces associated with a second-order shape transition from a spherical cap to a tethered vesicle. The second line is attributed to the detachment forces at which a first-order unbinding transition from a tethered shape to a free vesicle occurs.
Keywords: CELL-ADHESION; MEMBRANE ADHESION; DYNAMIC STRENGTH; MOLECULAR-BONDS; DETACHMENT; SPECTROSCOPY; MECHANICS; KINETICS; STICKERS; CLUSTERS

Force-induced growth of adhesion domains is controlled by receptor mobility - Smith, Ana-Suncana; Sengupta, Kheya; Goennenwein, Stefanie; Seifert, Udo; Sackmann, Erich (Proceedings of the National Academy of Sciences of the United States of America, 2008)
In living cells, adhesion structures have the astonishing ability to grow and strengthen under force. Despite the rising evidence of the importance of this phenomenon, little is known about the underlying mechanism. Here, we show that force-induced adhesion-strengthening can occur purely because of the thermodynamic response to the elastic deformation of the membrane, even in the absence of the actively regulated cytoskeleton of the cell, which was hitherto deemed necessary. We impose pN-forces on two fluid membranes, locally pre-adhered by RGD-integrin binding. One of the binding partners is always mobile whereas the mobility of the other can be switched on or off. immediate passive strengthening of adhesion structures occurs in both cases. When both binding partners are mobile, strengthening is aided by lateral movement of intact bonds as a transient response to force-induced membrane-deformation. By extending our microinterferometric technique to the suboptical regime, we show that the adhesion, as well as the resistance to force-induced de-adhesion, is greatly enhanced when both, rather than only one, of the binding partners are mobile. We formulate a theory that explains our observations by linking the macroscopic shape deformation with the microscopic formation of bonds, which further elucidates the importance of receptor mobility. We propose this fast passive response to be the first-recognition that triggers signaling events leading to mechanosensing in living cells.
Keywords: cell adhesion under force; dynamic reflection interference contrast microscopy; magnetic tweezers; mobile integrin-RGD bonds; model systems

Forces and shapes as determinants of micro-swimming: effect on synchronisation and the utilisation of drag - Pande, Jayant; Smith, Ana-Suncana (Soft Matter, 2015)
In this analytical study we demonstrate the richness of behaviour exhibited by bead-spring micro-swimmers, both in terms of known yet not fully explained effects such as synchronisation, and hitherto undiscovered phenomena such as the existence of two transport regimes where the swimmer shape has fundamentally different effects on the velocity. For this purpose we employ a micro-swimmer model composed of three arbitrarily-shaped rigid beads connected linearly by two springs. By analysing this swimmer in terms of the forces on the different beads, we determine the optimal kinematic parameters for sinusoidal driving, and also explain the pusher/puller nature of the swimmer. Moreover, we show that the phase difference between the swimmer's arms automatically attains values which maximise the swimming speed for a large region of the parameter space. Apart from this, we determine precisely the optimal bead shapes that maximise the velocity when the beads are constrained to be ellipsoids of a constant volume or surface area. On doing so, we discover the surprising existence of the aforementioned transport regimes in micro-swimming, where the motion is dominated by either a reduction of the drag force opposing the beads, or by the hydrodynamic interaction amongst them. Under some conditions, these regimes lead to counter-intuitive effects such as the most streamlined shapes forming locally the slowest swimmers.
Keywords: LOW-REYNOLDS-NUMBER; MOTORS; CILIA; DRIVEN; CARGO

"Foregrounding" - Sinding, Michael (2004)

Four-dimensional spinfoam quantum gravity with a cosmological constant: Finiteness and semiclassical limit - Han, Muxin (Physical Review D, 2021)
We present an improved formulation of 4-dimensional Lorentzian spinfoam quantum gravity with a cosmological constant. The construction of spinfoam amplitudes uses the state-integral model of PSL(2,C) Chern-Simons theory and the implementation of a simplicity constraint. The formulation has two key features: (1) spinfoam amplitudes are all finite, and (2) with suitable boundary data, the semiclassical asymptotics of the vertex amplitude has two oscillatory terms, with phase plus or minus the 4-dimensional Lorentzian Regge action with a cosmological constant for the constant curvature 4-simplex.
CRIS-Team Scopus Importer:2021-12-03

Four-valent vertex and the Penrose metric - Wasserka, Tony; Sahlmann, Hanno (2014)

Fractal analysis methods for solid alkane monolayer domains at SiO2?/air interfaces - Mecke, Klaus; et al. (Langmuir, 2005)
A systematic evaluation of various fractal analysis methods is essential for studying morphologies of finite and noisy experimental patterns such as domains of long chain alkanes at SiO2/air interfaces. The derivation of trustworthy fractal dimensions crucially relies on the definition of confidence intervals for the assumed scaling range. We demonstrate that the determination of the intervals can be improved largely by comparing the scaling behavior of different morphological measures (area, boundary, curvature). We show that the combination of area and boundary data from coarse-grained structures obtained with the box-counting method reveals clear confidence limits and thus credible morphological data. This also holds for the Minkowski density method. It also reveals the confidence range. Its main drawback, the larger swing-in period at the lower cutoff compared to the box-counting method, is compensated by more details on the scaling behavior of area, boundary, and curvature. The sandbox method is less recommendable. It essentially delivers the same data as box-counting, but it is more susceptible to finite size effects at the lower cutoff. It is found that the domain morphology depends on the surface coverage of alkanes. The individual domains at low surface coverage have a fractal dimension of approximate to1.7, whereas at coverages well above 50% the scaling dimension is 2 with a large margin of uncertainty at approximate to50% coverage. This change in morphology is attributed to a crossover from a growth regime dominated by diffusion-limited aggregation of individual domains to a regime where the growth is increasingly affected by annealing and the interaction of solid growth fronts which approach each other and thus compete for the alkane supply.

Fractional and integer excitations in quantum antiferromagnetic spin 1/2 ladders - Schmidt, Kai Phillip; et al. (Physical Review Letters, 2001)
Spectral densities are computed in unprecedented detail for quantum anti ferromagnetic spin 1/2 two-leg ladders. These results were obtained due to a major methodical advance achieved by optimally chosen unitary transformations. The approach is based on dressed integer excitations. Considerable weight is found at high energies in the two-particle sector. Precursors of fractional spinon physics occur supporting the conclusion that there is no necessity to resort to fractional excitations in order to describe features at higher energies.

Freezing and melting of a colloidal adsorbate on a 1D quasicrystalline substrate - Schmiedeberg, Michael; Roth, Johannes; Stark, Holger (Physical Review Letters, 2006)
Using Monte Carlo simulations and an extended Landau-Alexander-McTague theory, we demonstrate that colloids in a one-dimensional quasicrystalline potential order in triangular and rhombic-alpha crystalline phases. Increasing the strength of the potential further, a new type of light-induced melting is discovered that has its origin in the nonperiodicity of the potential. In contrast to reentrant melting in periodic potentials, the quasicrystalline potential melts the crystalline phases even when they already exist at zero potential.

From antiferromagnetic and hidden order to Pauli paramagnetism in UM2Si2 compounds with 5f electron duality - Amorese, Andrea; Sundermann, Martin; Leedahl, Brett; Marino, Andrea; Takegami, Daisuke; Gretarsson, Hlynur; Gloskovskii, Andrei; Schlueter, Christoph; Haverkort, Maurits W.; Huang, Yingkai; Szlawska, Maria; Kaczorowski, Dariusz; et al. (Proceedings of the National Academy of Sciences of the United States of America, 2020)
Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U [Formula: see text] electrons in U[Formula: see text] (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U [Formula: see text] configuration with the [Formula: see text] and [Formula: see text] quasi-doublet symmetry. The amount of the U 5[Formula: see text] configuration, however, varies considerably across the U[Formula: see text] series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in [Formula: see text] and [Formula: see text], the availability of orbital degrees of freedom needed for the hidden order in [Formula: see text] to occur, as well as the appearance of Pauli paramagnetism in [Formula: see text] A unified and systematic picture of the U[Formula: see text] compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered [Formula: see text] structure.
CRIS-Team Scopus Importer:2020-12-11
Keywords: hidden order; strongly correlated electron systems; uranium heavy fermions; X-ray spectroscopy

From classical to quantum gravity: Introduction to loop quantum gravity - Giesel, Kristina; Sahlmann, Hanno (Proceedings of Science, 2011)
We present an introduction to the canonical quantization of gravity performed in loop quantum gravity, based on lectures held at the 3rd quantum geometry and quantum gravity school in Zakopane in 2011. A special feature of this introduction is the inclusion of new proposals for coupling matter to gravity that can be used to deparametrize the theory, thus making its dynamics more tractable. The classical and quantum aspects of these new proposals are explained alongside the standard quantization of vacuum general relativity in loop quantum gravity.
CRIS-Team Scopus Importer:2022-05-09

From Classical To Quantum Gravity: Introduction to Loop Quantum Gravity - Giesel, Kristina; Sahlmann, Hanno (PoS - Proceedings of Science, 2011)
We present an introduction to the canonical quantization of gravity performed in loop quantum gravity, based on lectures held at the 3rd quantum geometry and quantum gravity school in Zakopane in 2011. A special feature of this introduction is the inclusion of new proposals for coupling matter to gravity that can be used to deparametrize the theory, thus making its dynamics more tractable. The classical and quantum aspects of these new proposals are explained alongside the standard quantization of vacuum general relativity in loop quantum gravity.

From groups and knots to black hole entropy - mathematical aspects of loop quantum gravity - Sahlmann, Hanno (World Scientific Publishing Co., 2013)
I will survey the formalism and main results of loop quantum gravity [1], [2] from a mathematical perspective. Then I take a closer look at the way black hole horizons are treated in the theory, by coupling a Chern-Simons theory on the horizon to the bulk degrees of freedom [3]. I will present some recent results on a new way to solve the self-duality equation involved directly in the quantum theory [4].
Keywords: Black holes; Duo isomorphism; Measures on spaces of connections; Quantum gravity; TQFT

From Kardar-Parisi-Zhang scaling to explosive desynchronization in arrays of limit-cycle oscillators - Lauter, Roland; Mitra, Aditi; Marquardt, Florian (Physical Review E, 2017)
Phase oscillator lattices subject to noise are one of the most fundamental systems in nonequilibrium physics. We have discovered a dynamical transition which has a significant impact on the synchronization dynamics in such lattices, as it leads to an explosive increase of the phase diffusion rate by orders of magnitude. Our analysis is based on the widely applicable Kuramoto-Sakaguchi model, with local couplings between oscillators. For one-dimensional lattices, we observe the universal evolution of the phase spread that is suggested by a connection to the theory of surface growth, as described by the Kardar-Parisi-Zhang (KPZ) model. Moreover, we are able to explain the dynamical transition both in one and two dimensions by connecting it to an apparent finite-time singularity in a related KPZ lattice model. Our findings have direct consequences for the frequency stability of coupled oscillator lattices.
CRIS-Team Scopus Importer:2023-03-27

From Water Solutions to Ionic Liquids with Solid State Nanopores as a Perspective to Study Transport and Translocation Phenomena - Marion, Sanjin; Vucemilovic-Alagic, Nataša; Spadina, Mario; Radenovic, Aleksandra; Smith, Ana-Suncana (Small, 2021)
Solid state nanopores are single-molecular devices governed by nanoscale physics with a broad potential for technological applications. However, the control of translocation speed in these systems is still limited. Ionic liquids are molten salts which are commonly used as alternate solvents enabling the regulation of the chemical and physical interactions on solid-liquid interfaces. While their combination can be challenging to the understanding of nanoscopic processes, there has been limited attempts on bringing these two together. While summarizing the state of the art and open questions in these fields, several major advances are presented with a perspective on the next steps in the investigations of ionic-liquid filled nanopores, both from a theoretical and experimental standpoint. By analogy to aqueous solutions, it is argued that ionic liquids and nanopores can be combined to provide new nanofluidic functionalities, as well as to help resolve some of the pertinent problems in understanding transport phenomena in confined ionic liquids and providing better control of the speed of translocating analytes.
CRIS-Team WoS Importer:2021-05-14

From White to Red: Electric-Field Dependent Chromaticity of Light-Emitting Electrochemical Cells based on Archetypal Porphyrins - Weber, Michael; Wittmann, Judith; Burger, Alexandra; Malcioglu, Osman; Segarra-Marti, Javier; Hirsch, Andreas; Coto, Pedro B.; Bockstedte, Michel; Costa, Ruben D. (Advanced Functional Materials, 2016)
The differences in the electroluminescence (EL) of red-emitting free-base (H2TPP) and Zn-metalated (ZnTPP) archetypal porphyrins are rationalized in light-emitting electrochemical cells by means of an electric-field dependent effect, leading to whitish and reddish devices, respectively. Although H2TPP shows superior electrochemical and photophysical features compared to ZnTPP, devices prepared with ZnTPP surprisingly stand out with a deep-red EL similar to its photoluminescence (PL), while H2TPP devices feature unexpected whitish EL. Standard arguments such as degradation, device architecture, device mechanism, and changes in the nature of the emitting excited states are discarded. Based on electrochemical impedance spectroscopy and first-principles electronic structure methods, we provide evidence that the EL originates from two H2TPP regioisomers, in which the inner ring H atoms are placed in collinear and vicinal configurations. The combination of their optical features provides an explanation for both the high- and low-energy EL features. Here, the emitting excited state nature is ascribed to the Q bands, since the Soret excited states remain high in energy. This contrasts to what is traditionally postulated in reports focused on H2TPP lighting devices. Hence, this work provides a new explanation for the nature of the high-energy EL band of H2TPP that might inspire future works focused on white-emitting molecular-based devices.
Keywords: collinear and vicinal regioisomers; electric-field dependent chromaticity; light-emitting electrochemical cells; tetraphenyl porphyrin; thin-film white-emitting sources

“From Words to Worldview: Reframing Narrative Genres in the French Revolution Debate.” - Sinding, Michael (Poetics Today, 2017)
Special issue on Situated Cognition and the Study of Culture This article draws together overlapping cognitive analyses of political thought, emotion and language, and shows how they can be supplemented with literary analyses of genre to illuminate the workings of the French Revolution Debate of 1790s Britain. It focuses on enriching George Lakoff’s theory of the multiple levels of framing in discourse, concentrating on the interplay of argument and narrative frames. Studies of emotion and mood in narrative genres are adapted to refine Lakoff’s account of narrative, making it more complex, systematic, and sensitive to historical context. Applying the revised theory, the essay characterizes contrasts between Edmund Burke’s and Thomas Paine’s thought at all levels of framing. It shows how their lexical frames for “Revolution” diverge as their main arguments craft opposing issue-defining frames for the central moral issue of Revolution-vs.-reform. Those arguments highlight different key figures and events, yet draw on similar narrative genres to frame them. Importantly, high genres of heroic romance inspire elevation towards one’s own side by celebrating victories and lamenting tragedies, and low genres of satire inspire contempt towards opponents by ridiculing deserved failures and absurd successes. Thus narrative genre ties surface-frame phrases like “rights of man” and “swinish multitude” to deep-frame assumptions about more fundamental concepts (human nature, society, government).
Keywords: framing; emotion; genre; politics; French Revolution Debate

“From World to Worldview: An Energy Principle of Psychosocial Dynamics.” - Sinding, Michael (The Cognitive Humanities: Embodied Mind in Literature and Culture, 2016)
To explain how cultural worldviews cohere, we need to develop principles of worldview structure. Image schemas and force dynamics must be central to worldview structure, since they are central conceptual structures of both metaphor and narrative, and both metaphor and narrative are central organising structures of worldview. However, the role of these conceptual structures in discourse has not been adequately studied, and they need to be developed (scaled up, supplemented and integrated) in order to represent rich and extended narrative and metaphoric thought adequately. A promising line of development is to link these structures with ‘intuitive ontology’ (especially ‘naïve physics’)—specifically, to characterise energy as a principle of conceptual structure for models of the physical world that can be used in metaphor and narrative to model the psychosocial world. I begin by considering William Blake’s Marriage of Heaven and Hell (1790) as a precursor vision of embodied cognition, as Blake declares that there is no soul distinct from body; and energy, which is life and delight, is from the body. I then examine visual and linguistic narrative representations of energy patterns, in popular culture examples, in Blake’s illustrations of good and wicked souls for Robert Blair’s poem The Grave (1805), and in a key scene in William Godwin’s novel Caleb Williams (1794). Turning to political argument and worldview, I show how Edmund Burke and Thomas Paine frame the French Revolution under contrasting models of psychosocial structures, causality and valuation. The metaphor scenarios (see Andreas Musolff, 'Metaphor Scenarios in Public Discourse', Metaphor & Symbol 21, 1 (2006), 23–38) in their arguments are of various ontologies and levels of schematicity: substances (property, body, parts, ties, mass), forces (tie, impulse), forceful movements (receive, hold, transmit, bind, circulate, pass-through, invigorate, dissolve, bring-together). Yet these arguments integrate the scenarios into broader psychosocial stories that are coherent and easily understood. Thus I propose a method for coordinating metaphor analysis at several levels of discourse: metaphor scenarios, metaphoric schema-structures, and super-schematic metaphoric narratives. Using this method, I characterise Burke’s and Paine’s central analogies for sociopolitical order; their moral priorities; and their moral blind spots. Throughout, I argue that it is only at the level of energy structure that we can specify how sequences of scenarios get integrated into patterns; and how coherent but opposite patterns of psychosocial energy underpin political models.
Keywords: metaphor; narrative; image schema; intuitive ontology; worldview

Fundamental Measure Theory for Inhomogeneous Fluids of Nonspherical Hard Particles - Hansen-Goos, Hendrik; Mecke, Klaus (Physical Review Letters, 2009)
Using the Gauss-Bonnet theorem we deconvolute exactly the Mayer f-function for arbitrarily shaped convex hard bodies in a series of tensorial weight functions, each depending only on the shape of a single particle. This geometric result allows the derivation of a free energy density functional for inhomogeneous hard-body fluids which reduces to Rosenfeld's fundamental measure theory [Phys. Rev. Lett. 63, 980 (1989)] when applied to hard spheres. The functional captures the isotropic-nematic transition for the hard-spherocylinder fluid in contrast with previous attempts. Comparing with data from Monte Carlo simulations for hard spherocylinders in contact with a planar hard wall, we show that the new functional also improves upon previous functionals in the description of inhomogeneous isotropic fluids.

Fundamental measure theory for non-spherical hard particles: predicting liquid crystal properties from the particle shape - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (Journal of Physics: Condensed Matter, 2016)
Density functional theory (DFT) for hard bodies provides a theoretical description of the effect of particle shape on inhomogeneous fluids. We present improvements of the DFT framework fundamental measure theory (FMT) for hard bodies and validate these improvements for hard spherocylinders. To keep the paper self-contained, we first discuss the recent advances in FMT for hard bodies that lead to the introduction of fundamental mixed measure theory (FMMT) in our previous paper (2015 Europhys. Lett. 109 26003). Subsequently, we provide an efficient semi-empirical alternative to FMMT and show that the phase diagram for spherocylinders is described with similar accuracy in both versions of the theory. Finally, we present a semi-empirical modification of FMMT whose predictions for the phase diagram for spherocylinders are in excellent quantitative agreement with computer simulation results.
Keywords: non-spherical particles; colloids; liquid crystals; continuum theory

Fundamental measure theory for smectic phases: Scaling behavior and higher order terms - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (Journal of Chemical Physics, 2014)
The recent extension of Rosenfeld's fundamental measure theory to anisotropic hard particles predicts nematic order of rod-like particles. Our analytic study of different aligned shapes provides new insights into the structure of this density functional, which is basically founded on experience with hard spheres. We combine scaling arguments with dimensional crossover and motivate a modified expression, which enables an appropriate description of smectic layering. We calculate the nematic-smectic-A transition of monodisperse hard spherocylinders with and without orientational degrees of freedom and present the equation of state and phase diagram including these two liquid crystalline phases in good agreement with simulations. We also find improved results related to the isotropic-nematic interface. We discuss the quality of empirical corrections and the convergence towards an exact second virial coefficient, including higher order terms. (C) 2014 AIP Publishing LLC.

Fundamental mixed measure theory for non-spherical colloids - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (EPL - Europhysics Letters, 2015)
Accurate predictions for the collective behavior of non-spherical colloids and nano-particles can guide the search for novel self-assembled materials. We derive a new type of density functional theory for mixtures of arbitrarily shaped convex hard bodies using integral geometry's translative integral formula and a scaling argument. Our fundamental mixed measure theory is exact in the low-density limit and does not require truncation or empirical parameters unlike previous functionals. Quantitatively correct results for hard spherocylinders validate our general approach. In particular, we present the phase diagram, including a qualitatively and quantitatively accurate smectic phase, and the isotropic-nematic interfacial tension. Copyright (C) EPLA, 2015

Gap Sensitivity Reveals Universal Behaviors in Optimized Photonic Crystal and Disordered Networks - Klatt, Michael; Steinhardt, Paul J.; Torquato, Salvatore (Physical Review Letters, 2021)
Through an extensive series of high-precision numerical computations of the optimal complete photonic band gap (PBG) as a function of dielectric contrast for a variety of crystal and disordered heterostructures, we reveal striking universal behaviors of the gap sensitivity , the first derivative of the optimal gap-to-midgap ratio . In particular, for all our crystal networks, takes a universal form that is well approximated by the analytic formula for a 1D quarter-wave stack, . Even more surprisingly, the values of for our disordered networks converge to for sufficiently large . A deeper understanding of the simplicity of this universal behavior may provide fundamental insights about PBG formation and guidance in the design of novel photonic heterostructures.
CRIS-Team Scopus Importer:2021-07-30

Gauge field theory coherent states (GCS): I. General properties - Thiemann, Thomas (Classical and Quantum Gravity, 2001)
The formalism introduced in this paper is immediately applicable also to lattice gauge theory in the presence of a (Minkowski) background structure on a possibly infinite lattice.

Gauge field theory coherent states (GCS): III. Ehrenfest theorems - Thiemann, Thomas; Winkler, Oliver (Classical and Quantum Gravity, 2001)
These results can be extended to all polynomials of elementary operators and to a certain non-polynomial function of the elementary operators associated with the volume operator of quantum general relativity. These findings are another step towards establishing that the infinitesimal quantum dynamics of quantum general relativity might, to lowest order in (h) over bar, indeed be given by classical general relativity.

Gauge field theory coherent states (GCS): II: Peakedness properties - Thiemann, Thomas; Winkler, Oliver (Classical and Quantum Gravity, 2001)
The text is supplemented by an appendix which contains extensive graphics in order to give a feeling for the so far unknown peakedness properties of the states constructed.

Gauge field theory coherent states (GCS): IV. Infinite tensor product and thermodynamical limit - Thiemann, Thomas; Winkler, Oliver (Classical and Quantum Gravity, 2001)
In the canonical approach to Lorentzian quantum general relativity in four spacetime dimensions an important step forward has been made by Ashtekar, Isham and Lewandowski some eight years ago through the introduction of a Hilbert space structure, which was later proved to be a faithful representation of the canonical commutation and adjointness relations of the quantum field algebra of diffeomorphism invariant gauge field theories by Ashtekar, Lewandowski, Marolf, Mourao and Thiemann. This Hilbert space, together with its generalization due to Baez and Sawin, is appropriate for semi-classical quantum general relativity if the spacetime is spatially compact. In the spatially non-compact case, however, an extension of the Hilbert space is needed in order to approximate metrics that are macroscopically nowhere degenerate. For this purpose, in this paper we apply the theory of the infinite tensor product (ITP) of Hilbert Spaces, developed by von Neumann more than sixty years ago, to quantum general relativity. The cardinality of the number of tensor product factors can take the value of any possible Cantor aleph, making this mathematical theory well suited to our problem in which a Hilbert space is attached to each edge of an arbitrarily complicated, generally infinite graph. The new framework opens access to a new arsenal of techniques, appropriate to describe fascinating physics such as quantum topology change, semi-classical quantum gravity, effective low-energy physics etc from the universal point of view of the ITP. In particular, the study of photons and gravitons propagating on fluctuating quantum spacetimes should now be in reach.

Gauge invariant canonical cosmological perturbation theory with geometrical clocks in extended phase-space - A review and applications. - Giesel, Kristina; Herzog, Adrian (International Journal of Modern Physics D, 2018)
The theory of cosmological perturbations is a well elaborated field. To deal with the diffeomorphism invariance of general relativity one generally introduces combinations of the metric and matter perturbations which are gauge invariant up to the considered order in the perturbations. For linear cosmological perturbations one works with the so-called Bardeen potentials widely used in this context. However, there exists no common procedure to construct gauge invariant quantities also for higher order perturbations. Usually, one has to find new gauge invariant quantities independently for each order in perturbation theory. With the relational formalism introduced by Rovelli and further developed by Dittrich and Thiemann, it is in principle possible to calculate manifestly gauge invariant quantities, that is quantities that are gauge invariant up to arbitrary order once one has chosen a set of so-called reference fields, often also called clock fields. This article contains a review of the relational formalism and its application to canonical general relativity following the work of Garcia, Pons, Sundermeyer and Salisbury. As the starting point for our application of this formalism to cosmological perturbation theory, we also review the Hamiltonian formulation of the linearized theory for perturbations around FLRW spacetimes. The main aim of our work will be to identify clock fields in the context of the relational formalism that can be used to reconstruct quantities like the Bardeen potential as well as the Mukhanov-Sasaki variable. This requires a careful analysis of the canonical formulation in the extended ADM-phase space where lapse and shift are treated as dynamical variables. The actual construction of such observables and further investigations thereof will be carried out in our companion paper.<br
Keywords: Canonical cosmological perturbation theory; relational framework; gauge invariance; general relativity; Dirac observables.

Gauge-invariant coherent states for loop quantum gravity: I. Abelian gauge groups - Bahr, Benjamin; Thiemann, Thomas (Classical and Quantum Gravity, 2009)
In this paper, we investigate the properties of gauge-invariant coherent states for loop quantum gravity, for the gauge group U(1). This is done by projecting the corresponding complexifier coherent states defined by Thiemann and Winklerto the gauge- invariant Hilbert space. This being the first step toward constructing physical coherent states, we arrive at a set of gauge- invariant states that approximate well the gauge-invariant degrees of freedom of Abelian loop quantum gravity (LQG). Furthermore, these states turn out to encode explicit information about the graph topology, and show the same pleasant peakedness properties known from the gauge-variant complexifier coherent states. In a companion paper, we will turn to the more sophisticated case of SU(2).

Gauge-invariant coherent states for loop quantum gravity: II. Non-Abelian gauge groups - Bahr, Benjamin; Thiemann, Thomas (Classical and Quantum Gravity, 2009)
This is the second paper concerning gauge-invariant coherent states for loop quantum gravity. Here, we deal with the gauge group SU(2), this being a significant complication compared to the Abelian U(1) case encountered in the previous article (Class. Quantum Grav. 26 045011). We study gauge-invariant coherent states on certain special graphs by analytical and numerical methods. We find that their overlap is Gauss peaked in gauge- invariant quantities, as long as states are not labeled by degenerate gauge orbits, i.e. points where the gauge- invariant configuration space has singularities. In these cases the overlaps are still concentrated around these points, but the peak profile exhibits a plateau structure. This shows how the semiclassical properties of the states are influenced by the geometry of the gauge-invariant phase space.

Gauge invariant variables for cosmological perturbation theory using geometrical clocks - Giesel, Kristina; Herzog, Adrian; Singh, Parampreet (Classical and Quantum Gravity, 2018)
Using the extended ADM-phase space formulation in the canonical framework we analyze the relationship between various gauge choices made in cosmological perturbation theory and the choice of geometrical clocks in the relational formalism. We show that various gauge invariant variables obtained in the conventional analysis of cosmological perturbation theory correspond to Dirac observables tied to a specific choice of geometrical clocks. As examples, we show that the Bardeen potentials and the Mukhanov-Sasaki variable emerge naturally in our analysis as observables when gauge fixing conditions are determined via clocks in the Hamiltonian framework. Similarly other gauge invariant variables for various gauges can be systematically obtained. We demonstrate this by analyzing five common gauge choices: longitudinal, spatially flat, uniform field, synchronous and comoving gauge. For all these, we apply the observable map in the context of the relational formalism and obtain the corresponding Dirac observables associated with these choices of clocks. At the linear order, our analysis generalizes the existing results in canonical cosmological perturbation theory twofold. On the one hand we can include also gauges that can only be analyzed in the context of the extended ADM-phase space and furthermore, we obtain a set of natural gauge invariant variables, namely the Dirac observables, for each considered choice of gauge conditions. Our analysis provides insights on which clocks should be used to extract the relevant natural physical observables both at the classical and quantum level. We also discuss how to generalize our analysis in a straightforward way to higher orders in the perturbation theory to understand gauge conditions and the construction of gauge invariant quantities beyond linear order.<br
Keywords: general relativity; cosmological perturbation theory; Dirac observables