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@article{faucris.256884037,
abstract = {We study the melting of long-range antiferromagnetic order in the Hubbard model after an interaction quench, using nonequilibrium dynamical mean-field theory. From previous studies, the system is known to quickly relax into a prethermal symmetry-broken state. Using a convergent truncation of the memory integrals in the Kadanoff Baym equations, we unravel the subsequent relaxation dynamics of this state over several orders of magnitude in time. At long times, the prethermal state can be characterized by a single slow variable, which is related to the conduction band population. The dynamics of this variable is highly nonlinear, with a pronounced speedup once the gap falls below a certain value. This behavior indicates that nonthermal order can be self-sustained on some timescale because of a thermalization bottleneck is provided by the gap opened by the long-range order itself. These results cannot be reproduced using simple Fermi's golden rule estimate for the evolution of the conduction band population, and are distinct from the conventional scenario for the relaxation of prethermal states, in which a slow thermalization follows a rapid prethermalization.},
author = {Picano, Antonio and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.165118},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-04-30},
peerreviewed = {Yes},
title = {{Accelerated} gap collapse in a {Slater} antiferromagnet},
volume = {103},
year = {2021}
}
@article{faucris.223994530,
abstract = {A fast time propagation method for nonequilibrium Green's functions (NEGF) based on the generalized Kadanoff–Baym Ansatz (GKBA) is applied to a lattice system with a symmetry-broken equilibrium phase, namely an excitonic insulator (EI). The adiabatic preparation of a correlated symmetry-broken initial state from a Hartree–Fock wave function within GKBA is assessed by comparing with a solution of the imaginary-time Dyson equation. It is found that it is possible to reach a symmetry-broken correlated initial state with nonzero excitonic order parameter by the adiabatic switching (AS) procedure. It is discussed under which circumstances this is possible in practice within reasonably short switching times.},
author = {Tuovinen, Riku and Golež, Denis and Schüler, Michael and Werner, Philipp and Eckstein, Martin and Sentef, Michael A.},
doi = {10.1002/pssb.201800469},
faupublication = {yes},
journal = {physica status solidi (b)},
keywords = {excitonic insulators; generalized Kadanoff–Baym Ansatz; nonequilibrium Green's function; time propagation},
note = {CRIS-Team Scopus Importer:2019-08-06},
peerreviewed = {Yes},
title = {{Adiabatic} {Preparation} of a {Correlated} {Symmetry}-{Broken} {Initial} {State} with the {Generalized} {Kadanoff}–{Baym} {Ansatz}},
volume = {256},
year = {2019}
}
@article{faucris.109755844,
abstract = {Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits. We argue that this distribution form, that occurs only at the Dirac point, lies at the heart of the observation of both metallic and insulating states in bilayer graphene.},
author = {Shallcross, Sam and Sharma, Sangeeta and Weber, Heiko B.},
doi = {10.1038/s41467-017-00397-8},
faupublication = {yes},
journal = {Nature Communications},
pages = {342},
peerreviewed = {Yes},
title = {{Anomalous} {Dirac} point transport due to extended defects in bilayer graphene},
url = {https://www.nature.com/articles/s41467-017-00397-8},
volume = {8},
year = {2017}
}
@article{faucris.118768584,
author = {Kißlinger, Ferdinand and Popp, Matthias Albert and Jobst, Johannes and Shallcross, Sam and Weber, Heiko B.},
doi = {10.1002/andp.201700048},
faupublication = {yes},
journal = {Annalen Der Physik},
peerreviewed = {Yes},
title = {{Charge}-carrier transport in large-area epitaxial graphene},
volume = {2017},
year = {2017}
}
@article{faucris.246692028,
abstract = {We investigate the equilibrium state and the collective modes of an excitonic insulator (EI) in a Fabry-Pérot cavity. In an EI, two bands of a semiconductor or semimetal spontaneously hybridize due to the Coulomb interaction between electrons and holes, leading to the opening of a gap. The coupling to the electromagnetic field reduces the symmetry of the system with respect to phase rotations of the excitonic order parameter from U(1) to Z2. While the reduction to a discrete symmetry would, in general, lead to a gapped phase mode and enhance the stability of the ordered phase, the coupling to the cavity leaves the mean-field ground state unaffected. Its energy remains invariant under U(1) phase rotations, in spite of the lower Z2 symmetry imposed by the cavity. In a dipolar gauge, this can be traced back to the balancing of the linear light-matter coupling and the dipolar self-interaction at zero frequency. At nonzero frequency, however, the collective excitations do reflect the lower Z2 symmetry. While our model is studied using a mean-field decoupling of the light-matter approximation (which is exact in the single-mode limit), the results show that fluctuations beyond mean field could play a crucial role in finding the true phase at finite temperature.},
author = {Lenk, Katharina and Eckstein, Martin},
doi = {10.1103/PhysRevB.102.205129},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2020-12-11},
peerreviewed = {Yes},
title = {{Collective} excitations of the {U} (1)-symmetric exciton insulator in a cavity},
volume = {102},
year = {2020}
}
@article{faucris.243948111,
abstract = {We investigate out-of-equilibrium dynamics in an excitonic insulator (EI) with a finite-momentum pairing perturbed by a laser-pulse excitation and a sudden coupling to fermionic baths. The transient dynamics of the excitonic order parameter is resolved using the full nonequilibrium Green's function approach and the generalized Kadanoff-Baym ansatz (GKBA) within the second-order Born approximation. The comparison between the two approaches after a laser-pulse excitation shows a good agreement in the weak and the intermediate photodoping regime. In contrast, the laser-pulse dynamics resolved by the GKBA does not show a complete melting of the excitonic order after a strong excitation. Instead we observe persistent oscillations of the excitonic order parameter with a predominant frequency given by the renormalized equilibrium band gap. This anomalous behavior can be overcome within the GKBA formalism by coupling to an external bath, which leads to a transition of the EI system toward the normal state. We analyze the long-time evolution of the system and distinguish decay timescales related to dephasing and thermalization.},
author = {Tuovinen, Riku and Golez, Denis and Eckstein, Martin and Sentef, Michael A.},
doi = {10.1103/PhysRevB.102.115157},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2020-10-16},
peerreviewed = {Yes},
title = {{Comparing} the generalized {Kadanoff}-{Baym} ansatz with the full {Kadanoff}-{Baym} equations for an excitonic insulator out of equilibrium},
volume = {102},
year = {2020}
}
@article{faucris.265186445,
abstract = {We explore a source-free local spin density approximation (LSDA)+U functional within density functional theory for its capabilities in describing noncollinear spin textures; capturing the noncollinear magnetic ground state of the spinel vanadates AV(2)O(4) (A = Mn, Fe, and Co) remains an outstanding challenge for state-of-the-art ab initio methods. We demonstrate that both the noncollinear spin texture, as well as the magnitude of local moments, are captured, provided the source term (i.e., magnetic monopole term) is removed from the exchange-correlation magnetic field B-XC. This suggests that for treatment of strongly correlated magnetic materials within the LSDA+U method the subtraction of the unphysical magnetic monopole term from the B-XC is essential.},
author = {Krishna, Jyoti and Singh, N. and Shallcross, Sam and Dewhurst, J. K. and Gross, E. K. U. and Maitra, T. and Sharma, S.},
doi = {10.1103/PhysRevB.100.081102},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-10-18},
peerreviewed = {Yes},
title = {{Complete} description of the magnetic ground state in spinel vanadates},
volume = {100},
year = {2019}
}
@article{faucris.213255033,
abstract = {The influence of an intramolecular proton transfer reaction on the conductance of a molecular junction is investigated employing a generic model, which includes the effects of the electric field of the gate and leads electrodes and the coupling to a dissipative environment. Using a quantum master equation approach it is shown that, depending on the localization of the proton, the junction exhibits a high or low current state, which can be controlled by external electric fields. Considering different regimes, which range from weak to strong hydrogen bonds in the proton transfer complex and comprise situations with high and low barriers, necessary preconditions to achieve control are analyzed. The results show that systems with a weak hydrogen bond and a significant energy barrier for the proton transfer can be used as molecular transistors or diodes.},
author = {Hofmeister, Chriszandro and Coto, Pedro B. and Thoss, Michael},
doi = {10.1063/1.4974512},
faupublication = {yes},
journal = {Journal of Chemical Physics},
note = {EAM Import::2019-03-13},
peerreviewed = {unknown},
title = {{Controlling} the conductance of molecular junctions using proton transfer reactions: {A} theoretical model study},
volume = {146},
year = {2017}
}
@article{faucris.295407693,
abstract = {We investigate the impact of a bosonic degree of freedom on Yu-Shiba-Rusinov states emerging from a magnetic impurity in a conventional superconductor. Starting from the Anderson impurity model, we predict that an additional p-wave conduction band channel opens up if a bosonic mode is coupled to the tunneling between impurity and host, which implies an additional pair of odd-parity Yu-Shiba-Rusinov states. The bosonic mode can be a vibrational mode or the electromagnetic field in a cavity. The exchange couplings in the two channels depend sensitively on the state of the bosonic mode (ground state, few quanta, or classically driven Floquet state), which opens possibilities for phononics or photonics control of such systems, with a rich variety of ground and excited states.},
author = {Müller, Hartmut and Eckstein, Martin and Viola Kusminskiy, Silvia},
doi = {10.1103/PhysRevLett.130.106905},
faupublication = {yes},
journal = {Physical Review Letters},
note = {CRIS-Team Scopus Importer:2023-04-07},
peerreviewed = {Yes},
title = {{Control} of {Yu}-{Shiba}-{Rusinov} {States} through a {Bosonic} {Mode}},
volume = {130},
year = {2023}
}
@article{faucris.121011484,
abstract = {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.},
author = {Schmid, Frank and Pensl, Gerhard and Bockstedte, Michel Georg and Mattausch, Alexander and Pankratov, Oleg and Ohshima, T. and Itoh, H. and Weber, Heiko B. and Reshanov, Sergey},
doi = {10.1103/PhysRevB.74.245212},
faupublication = {yes},
journal = {Physical Review B},
note = {UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.IAP.LAP.deacti},
pages = {245212},
peerreviewed = {Yes},
title = {{Deactivation} of nitrogen donors in silicon carbide},
volume = {B 74},
year = {2006}
}
@article{faucris.265175071,
abstract = {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.},
author = {Weckbecker, Dominik and Gupta, Reena and Rost, Fabian and Sharma, S. and Shallcross, Sam},
doi = {10.1103/PhysRevB.99.195405},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-10-18},
peerreviewed = {Yes},
title = {{Dislocation} and node states in bilayer graphene systems},
volume = {99},
year = {2019}
}
@article{faucris.246976067,
abstract = {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.},
author = {Valmispild, V. N. and Dutreix, C. and Eckstein, Martin and Katsnelson, M. and Lichtenstein, A. and Stepanov, E. A.},
doi = {10.1103/PhysRevB.102.220301},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2020-12-18},
peerreviewed = {Yes},
title = {{Dynamically} induced doublon repulsion in the {Fermi}-{Hubbard} model probed by a single-particle density of states},
volume = {102},
year = {2020}
}
@article{faucris.287483883,
abstract = {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.},
author = {Lenk, Katharina and Li, Jiajun and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.106.245124},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2023-01-13},
peerreviewed = {Yes},
title = {{Dynamical} mean-field study of a photon-mediated ferroelectric phase transition},
volume = {106},
year = {2022}
}
@article{faucris.284492605,
abstract = {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.},
author = {Marino, Jamir and Eckstein, Martin and Foster, Matthew S. and Rey, Ana Maria},
doi = {10.1088/1361-6633/ac906c},
faupublication = {yes},
journal = {Reports on Progress in Physics},
keywords = {collisionless pre-thermal states; dynamical phase transitions; isolated quantum systems},
note = {CRIS-Team Scopus Importer:2022-11-04},
peerreviewed = {Yes},
title = {{Dynamical} phase transitions in the collisionless pre-thermal states of isolated quantum systems: {Theory} and experiments},
volume = {85},
year = {2022}
}
@article{faucris.117842384,
abstract = {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.},
author = {Prucker, Veronika and Rubio-Pons, Oscar and Bockstedte, Michel Georg and Wang, Haobin and Brana Coto, Pedro and Thoss, Michael},
doi = {10.1021/jp4091848},
faupublication = {yes},
journal = {Journal of Physical Chemistry C},
note = {UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.ITP.ppem.dynami},
pages = {25334-25342},
peerreviewed = {Yes},
title = {{Dynamical} {Simulation} of {Electron} {Transfer} {Processes} in {Alkanethiolate} {Self}-{Assembled} {Monolayers} at the {Au}(111) {Surface}},
volume = {117},
year = {2013}
}
@article{faucris.223566574,
abstract = {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.},
author = {Golez, Denis and Boehnke, Lewin and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.100.041111},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2019-08-02},
peerreviewed = {Yes},
title = {{Dynamics} of photodoped charge transfer insulators},
volume = {100},
year = {2019}
}
@article{faucris.274937027,
abstract = {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.},
author = {Li, Jiajun and Schamriß, Lukas and Eckstein, Martin},
doi = {10.1103/PhysRevB.105.165121},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2022-05-13},
peerreviewed = {Yes},
title = {{Effective} theory of lattice electrons strongly coupled to quantum electromagnetic fields},
volume = {105},
year = {2022}
}
@article{faucris.236523784,
abstract = {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.},
author = {Malcioglu, Osman and Bechis, Irene and Bockstedte, Michel Georg},
doi = {10.1039/c9cp06040e},
faupublication = {yes},
journal = {Physical Chemistry Chemical Physics},
note = {CRIS-Team WoS Importer:2020-03-27},
pages = {3825-3830},
peerreviewed = {Yes},
title = {{Effect} of crystallization on the electronic and optical properties of archetypical porphyrins},
volume = {22},
year = {2020}
}
@article{faucris.248105465,
abstract = {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.},
author = {Bittner, Nikolaj and Golez, Denis and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.102.235169},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-01-22},
peerreviewed = {Yes},
title = {{Effects} of frustration on the nonequilibrium dynamics of photoexcited lattice systems},
volume = {102},
year = {2020}
}
@article{faucris.290212142,
author = {Weber, Michael and Wittmann, Judith and Burger, Alexandra and Malcioglu, Osman and Segarra-Martí, Javier and Hirsch, Andreas and Coto, Pedro B. and Bockstedte, Michel Georg and Costa, Ruben Dario},
doi = {10.1002/adfm.201670243},
faupublication = {yes},
journal = {Advanced Functional Materials},
keywords = {collinear and vicinal regioisomers; electric-field dependent chromaticity; light-emitting electrochemical cells; tetraphenyl porphyrin; thin-film white-emitting sources},
note = {CRIS-Team Scopus Importer:2023-03-07},
pages = {6736-},
peerreviewed = {Yes},
title = {{Electroluminescence}: {From} {White} to {Red}: {Electric}-{Field} {Dependent} {Chromaticity} of {Light}-{Emitting} {Electrochemical} {Cells} based on {Archetypal} {Porphyrins} ({Adv}. {Funct}. {Mater}. 37/2016)},
volume = {26},
year = {2016}
}
@article{faucris.239072368,
abstract = {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.},
author = {Li, Jiajun and Golez, Denis and Mazza, Giacomo and Millis, Andrew J. and Georges, Antoine and Eckstein, Martin},
doi = {10.1103/PhysRevB.101.205140},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2020-06-05},
peerreviewed = {Yes},
title = {{Electromagnetic} coupling in tight-binding models for strongly correlated light and matter},
volume = {101},
year = {2020}
}
@article{faucris.249336713,
abstract = {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.},
author = {Stahl, Christopher and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.035116},
faupublication = {yes},
journal = {Physical Review B},
month = {Jan},
note = {CRIS-Team Scopus Importer:2021-02-12},
peerreviewed = {Yes},
title = {{Electronic} and fluctuation dynamics following a quench to the superconducting phase},
volume = {103},
year = {2021}
}
@article{faucris.122935164,
author = {Classen, Andrej and Pöschel, Rebecca and di Filippo, Gianluca and Fauster, Thomas and Malcioglu, Osman and Bockstedte, Michel Georg},
doi = {10.1103/PhysRevB.95.115414},
faupublication = {yes},
journal = {Physical Review B},
pages = {115414},
peerreviewed = {Yes},
title = {{Electronic} structure of tetraphenylporphyrin layers on {Ag}(100)},
url = {http://link.aps.org/doi/10.1103/PhysRevB.95.115414},
volume = {95},
year = {2017}
}
@article{faucris.228297797,
abstract = {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.},
author = {Werner, Philipp and Li, Jiajun and Golez, Denis and Eckstein, Martin},
doi = {10.1103/PhysRevB.100.155130},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2019-10-25},
peerreviewed = {Yes},
title = {{Entropy}-cooled nonequilibrium states of the {Hubbard} model},
volume = {100},
year = {2019}
}
@article{faucris.244862189,
abstract = {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.},
author = {Li, Jiajun and Golez, Denis and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.102.165136},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2020-11-06},
peerreviewed = {Yes},
title = {eta-paired superconducting hidden phase in photodoped {Mott} insulators},
volume = {102},
year = {2020}
}
@article{faucris.261048375,
abstract = {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.},
author = {Grandi, Francesco and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.245117},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-07-02},
peerreviewed = {Yes},
title = {{Fluctuation} control of nonthermal orbital order},
volume = {103},
year = {2021}
}
@article{faucris.107060624,
abstract = {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.},
author = {Weber, Michael and Wittmann, Judith and Burger, Alexandra and Malcioglu, Osman and Segarra-Marti, Javier and Hirsch, Andreas and Coto, Pedro B. and Bockstedte, Michel and Costa, Ruben D.},
doi = {10.1002/adfm.201602252},
faupublication = {yes},
journal = {Advanced Functional Materials},
keywords = {collinear and vicinal regioisomers; electric-field dependent chromaticity; light-emitting electrochemical cells; tetraphenyl porphyrin; thin-film white-emitting sources},
pages = {6737-6750},
peerreviewed = {Yes},
title = {{From} {White} to {Red}: {Electric}-{Field} {Dependent} {Chromaticity} of {Light}-{Emitting} {Electrochemical} {Cells} based on {Archetypal} {Porphyrins}},
volume = {26},
year = {2016}
}
@article{faucris.264073462,
abstract = {We derive a general relation between the stacking vector u describing the relative shift of two layers of bilayer graphene and the Chern index. We find C = nu(1 - sign(vertical bar V-AB vertical bar - vertical bar V-BA vertical bar)), where nu is a valley index and vertical bar V-alpha beta vertical bar the absolute value of the u dependent stacking potentials that uniquely determine the interlayer interaction; AA stacking plays no role in the topological character. With this expression we show that while ideal and relaxed minimally twisted bilayer graphene appear so distinct as to be almost different materials, their Chern index maps are, remarkably, identical. The topological physics of this material is thus strongly robust to lattice relaxations.},
author = {Theil, Simon and Fleischmann, Maximilian and Gupta, R. and Rost, Fabian and Wullschläger, Florian and Sharma, S. and Meyer, Bernd and Shallcross, S.},
doi = {10.1103/PhysRevB.104.125412},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-09-17},
peerreviewed = {Yes},
title = {{General} relation between stacking order and {Chern} index: {A} topological map of minimally twisted bilayer graphene},
volume = {104},
year = {2021}
}
@masterthesis{faucris.320671726,
abstract = {In this thesis we consider the coupling of Maxwell theory to linearised gravity and derive a master
equation which suggests gravitationally induced decoherence on vector fields. The model is based
on the linear Hamiltonian formulation of general relativity with the use of Ashtekar variables.
The matter is coupled to linearised gravity, consistently using the framework of post-Minkowski
formalism. In order to formulate the model at the gauge invariant level, the relational formalism
is used. Therefore, we will consistently connect linearised gravity to the constrained system of
Maxwell’s theory by constructing suitable geometrical and electromagnetic reference fields. This
will be used to construct Dirac observables for the coupled system. Then we will use a reduced
phase space quantisation on the Fock space. To construct a TCL master equation we apply
the projecting operator technique with the time-convolutionless approach to the model, using a
Gibbs state as the initial state for linearised gravity. All assumptions and approximations in the
intermediate steps will be carefully analysed. In addition, the final TCL master equation is formulated in terms of thermal Wightmann functions and is not automatically of the Lindblad type,
which is often the starting point for phenomenological models, and in contrast to the existing
literature. For the derived master equation, we will also discuss why the Markov approximation
is not easily applicable. Furthermore, we will motivate that the formalism used in this thesis to
couple a constrained system to linearised gravity could be generalised to all Yang-Mills theories.

2YZ with Y = (Ni, Co, Pt), and Co2YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co2NiZ, Co2PtZ, and Fe2PtZ families the cubic phase is always, at T = 0, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe2NiZ and Fe2CoZ families this is the case for only 2 compounds - Fe2NiGe and Fe2NiSn. For all compounds in which a tetragonal distortion occurs we calculate the magnetocrystalline anisotropy energy (MAE) finding remarkably large values for the Pt containing Heuslers, but also large values for a number of the other compounds (e.g. Co2NiGa has an MAE of -2.38 MJ m^{-3}). The tendency to a tetragonal distortion we find to be strongly correlated with a high density of states (DOS) at the Fermi level in the cubic phase. As a corollary to this fact we observe that upon doping compounds for which the cubic structure is stable such that the Fermi level enters a region of high DOS, a tetragonal distortion is induced and a correspondingly large value of the MAE is then observed.},
author = {Matsushita, Y-I and Madjarova, Galia and Dewhurst, J. K. and Shallcross, Sam and Felser, Claudia and Sharma, Sangeeta and Gross, E. K. U.},
doi = {10.1088/1361-6463/aa5441},
faupublication = {no},
journal = {Journal of Physics D: Applied Physics},
keywords = {ab initio calculations; Heusler compunds; tetragonal distortion},
note = {CRIS-Team Scopus Importer:2022-04-14},
peerreviewed = {Yes},
title = {{Large} magnetocrystalline anisotropy in tetragonally distorted {Heuslers}: {A} systematic study},
volume = {50},
year = {2017}
}
@article{faucris.230624415,
abstract = {An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature. Strongly correlated Fermi liquids and symmetry-broken states could thus be produced by dipolar excitations. Using nonequilibrium dynamical mean field theory, we show that suitably designed chirped pulses may realize this cooling effect. In particular, we demonstrate the emergence of antiferromagnetic order in a system which is initially in a weakly correlated state above the maximum Néel temperature. Our work suggests a general strategy for inducing strong correlation phenomena in periodically modulated atomic gases in optical lattices or light-driven materials.},
author = {Werner, Philipp and Eckstein, Martin and Müller, Markus and Refael, Gil},
doi = {10.1038/s41467-019-13557-9},
faupublication = {yes},
journal = {Nature Communications},
note = {CRIS-Team Scopus Importer:2019-12-17},
peerreviewed = {Yes},
title = {{Light}-induced evaporative cooling of holes in the {Hubbard} model},
volume = {10},
year = {2019}
}
@article{faucris.325729900,
abstract = {Sr2IrO4 has attracted considerable attention due to its structural and electronic similarities to La2CuO4, the parent compound of high-Tc superconducting cuprates. It was proposed as a strong spin-orbit-coupled Jeff = 1/2 Mott insulator, but the Mott nature of its insulating ground state has not been conclusively established. Here, we use ultrafast laser pulses to realize an insulator-metal transition in Sr2IrO4 and probe the resulting dynamics using time- and angle-resolved photoemission spectroscopy. We observe a gap closure and the formation of weakly renormalized electronic bands in the gap region. Comparing these observations to the expected temperature and doping evolution of Mott gaps and Hubbard bands provides clear evidence that the insulating state does not originate from Mott correlations. We instead propose a correlated band insulator picture, where antiferromagnetic correlations play a key role in the gap opening. More broadly, our results demonstrate that energy-momentum-resolved nonequilibrium dynamics can be used to clarify the nature of equilibrium states in correlated materials.},
author = {Choi, Dongsung and Yue, Changming and Azoury, Doron and Porter, Zachary and Chen, Jiyu and Petocchi, Francesco and Baldini, Edoardo and Lv, Baiqing and Mogi, Masataka and Su, Yifan and Wilson, Stephen D. and Eckstein, Martin and Werner, Philipp and Gedik, Nuh},
doi = {10.1073/pnas.2323013121},
faupublication = {yes},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
keywords = {cluster dynamical mean-field theory; correlated band insulator; light-induced insulator–metal transition; time- and angle-resolved photoemission spectroscopy},
note = {CRIS-Team Scopus Importer:2024-07-19},
pages = {e2323013121},
peerreviewed = {Yes},
title = {{Light}-induced insulator-metal transition in {Sr2IrO4} reveals the nature of the insulating ground state},
volume = {121},
year = {2024}
}
@article{faucris.122286824,
abstract = {The magnetoresistance of conductors usually has a quadratic dependence on magnetic field(1), however, examples exist of non-saturating linear behaviour in diverse materials(2-6). Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure(7,8). Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations(9,10). We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.},
author = {Kißlinger, Ferdinand and Ott, Christian and Heide, Christian and Kampert, Erik and Butz, Benjamin and Spiecker, Erdmann and Shallcross, Sam and Weber, Heiko B.},
doi = {10.1038/NPHYS3368},
faupublication = {yes},
journal = {Nature Physics},
pages = {650-+},
peerreviewed = {Yes},
title = {{Linear} magnetoresistance in mosaic-like bilayer graphene},
volume = {11},
year = {2015}
}
@article{faucris.285009309,
abstract = {We present a formalism based on nonequilibrium dynamical mean-field theory (DMFT) which allows to compute the time-resolved x-ray absorption spectrum (XAS) of photoexcited solids. By applying this formalism to the photodoped half-filled and quarter-filled two-orbital Hubbard models in the Mott insulating regime we clarify how the time-resolved XAS signal reflects the nonequilibrium population of different local states. Apart from the missing broadening associated with continuum excitations, the atomic XAS spectrum computed with the nonthermal state populations provides a good approximation to the full nonequilibrium DMFT result. This suggests a route to combine the accurate DMFT description of nonequilibrium states of solids with cluster calculations of the XAS signal.},
author = {Werner, Philipp and Golez, Denis and Eckstein, Martin},
doi = {10.1103/PhysRevB.106.165106},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2022-11-11},
peerreviewed = {Yes},
title = {{Local} interpretation of time-resolved x-ray absorption in {Mott} insulators: {Insights} from nonequilibrium dynamical mean-field theory},
volume = {106},
year = {2022}
}
@article{faucris.246707175,
abstract = {Intertwined orders exist ubiquitously in strongly correlated electronic systems and lead to intriguing phenomena in quantum materials. In this Letter, we explore the unique opportunity of manipulating intertwined orders through entangling electronic states with quantum light. Using a quantum Floquet formalism to study the cavity-mediated interaction, we show the vacuum fluctuations effectively enhance the charge-density-wave correlation, giving rise to a phase with entangled electronic order and photon coherence, with putative superradiant behaviors in the thermodynamic limit. Furthermore, upon injecting even one single photon in the cavity, different orders, including s-wave and eta-paired superconductivity, can be selectively enhanced. Our study suggests a new and generalizable pathway to control intertwined orders and create light-matter entanglement in quantum materials. The mechanism and methodology can be readily generalized to more complicated scenarios.},
author = {Li, Jiajun and Eckstein, Martin},
doi = {10.1103/PhysRevLett.125.217402},
faupublication = {yes},
journal = {Physical Review Letters},
note = {CRIS-Team WoS Importer:2020-12-11},
peerreviewed = {Yes},
title = {{Manipulating} {Intertwined} {Orders} in {Solids} with {Quantum} {Light}},
volume = {125},
year = {2020}
}
@article{faucris.273556520,
abstract = {The Keldysh formalism for nonequilibrium Green's functions is a powerful theoretical framework for the description of the electronic structure, spectroscopy, and dynamics of strongly correlated systems. However, the underlying Kadanoff-Baym equations (KBE) for the two-time Keldysh Green's functions involve a memory kernel, which results in a high computational cost for long simulation times tmax, with a cubic scaling of the computation time with tmax. Truncation of the memory kernel can reduce the computational cost to linear scaling with tmax, but the required memory times will depend on the model and the diagrammatic approximation to the self-energy. We explain how a truncation of the memory kernel can be incorporated into the time-propagation algorithm to solve the KBE, and investigate the systematic truncation of the memory kernel for the Hubbard model in different parameter regimes, and for different diagrammatic approximations. The truncation is easier to control within dynamical mean-field solutions, where it is applied to a momentum-independent self-energy. Here, simulation times up to two orders of magnitude longer are accessible both in the weak and strong coupling regime, allowing for a study of long-time phenomena such as the crossover between prethermalization and thermalization dynamics.},
author = {Stahl, Christopher and Dasari, Nagamalleswara Rao and Li, Jiajun and Picano, Antonio and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.105.115146},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2022-04-22},
peerreviewed = {Yes},
title = {{Memory} truncated {Kadanoff}-{Baym} equations},
volume = {105},
year = {2022}
}
@article{faucris.247772833,
abstract = {The potential of proton transfer reactions as a fundamental mechanism to realize a nanoscale molecular transistor is investigated. Employing density functional theory and the nonequilibrium Green's function formalism, we identify molecule-graphene nanojunctions, which exhibit high- and low-conducting states depending on the specific location of protons in the molecular bridge. In addition, we show that an electrostatic gate field can control the proton transfer process and thus allow specific conductance states to be selected. In this way, the current in the junction can be switched on and off as in a field-effect transistor. The underlying mechanism is analyzed in detail.},
author = {Weckbecker, Dominik and Coto, P. B. and Thoss, M.},
doi = {10.1021/acs.jpclett.0c03405},
faupublication = {yes},
journal = {Journal of Physical Chemistry Letters},
note = {CRIS-Team Scopus Importer:2021-01-15},
pages = {413-417},
peerreviewed = {Yes},
title = {{Molecular} {Transistor} {Controlled} through {Proton} {Transfer}},
year = {2021}
}
@article{faucris.216901458,
abstract = {We study the dynamical behavior of doped electronic systems subject to a global ramp of the repulsive Hubbard interaction. We start with formulating a real-time generalization of the fluctuation-exchange approximation. Implementing this numerically, we investigate the weak-coupling regime of the Hubbard model both in the electron-doped and hole-doped regimes. The results show that both local and nonlocal (momentum-dependent) observables evolve toward a thermal state, although the temperature of the final state depends on the ramp duration and the band filling. We further reveal a momentum-dependent relaxation rate of the distribution function in doped systems and trace back its physical origin to the anisotropic self-energies in the momentum space.},
author = {Sayyad, Sharareh and Tsuji, Naoto and Vaezi, Abolhassan and Capone, Massimo and Eckstein, Martin and Aoki, Hideo},
doi = {10.1103/PhysRevB.99.165132},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2019-05-03},
peerreviewed = {Yes},
title = {{Momentum}-dependent relaxation dynamics of the doped repulsive {Hubbard} model},
volume = {99},
year = {2019}
}
@article{faucris.249335206,
abstract = {Porphyrins are key elements in organic-inorganic hybrid systems for a wide range of applications. Understanding their interaction with the substrate gives a handle on structural and electronic device properties. Here we investigate a single transition-metal porphyrin, namely Co(ii)-tetraphenylporphyrin (CoTPP), on the MgO(100) surface and the effect of multilayer film formation within hybrid density-functional theory and many-body perturbation theory. We focus on the relevant adsorption sites, simulate their photoemission spectra as a key fingerprint and compare with experiments on MgO(100) films on Ag(100). While we find only weak interaction between the cobalt centre and terrace sites on the MgO(100) surface, a strong interaction manifests itself with the low-coordinated sites. This leads to distinct features in both the valence and core-level regions of the electronic structure, as observed in the ultraviolet and X-ray photoemission spectra, corroborated by simulated spectra and calculated cobalt core-level shifts. Our work thus demonstrates the relevance of morphology-related low-coordinated sites and their properties in the adsorption of CoTPP on the MgO(100) surface.},
author = {Ninova, Silviya and Malcıoğlu, Osman Barış and Auburger, Philipp and Franke, Matthias and Lytken, Ole and Steinrück, Hans-Peter and Bockstedte, Michel},
doi = {10.1039/d0cp04859c},
faupublication = {yes},
journal = {Physical Chemistry Chemical Physics},
month = {Jan},
note = {CRIS-Team Scopus Importer:2021-02-12},
pages = {2105-2116},
peerreviewed = {Yes},
title = {{Morphology} dependent interaction between {Co}(ii)-tetraphenylporphyrin and the {MgO}(100) surface},
volume = {23},
year = {2021}
}
@article{faucris.230866278,
abstract = {We study the dynamics of charge-transfer insulators after a photoexcitation using the three-band Emery model which is relevant for the description of cuprate superconductors. We provide a detailed derivation of the nonequilibrium extension of the multiband GW+EDMFT formalism and the corresponding downfolding procedure. The Peierls construction of the electron-light coupling is generalized to the multiband case resulting in a gauge invariant combination of the Peierls intraband acceleration and dipolar interband transitions. We use the formalism to study momentum-dependent (inverse) photoemission spectra and optical conductivities. The time-resolved spectral function shows a strong renormalization of the charge-transfer gap and a substantial broadening of some of the bands. While the upper Hubbard band exhibits a momentum-dependent broadening, an almost rigid band shift is observed for the ligand bands. The inverse photoemission spectrum reveals that the inclusion of nonlocal and interband charge fluctuations results in a very fast relaxation of the holes to the top of the Zhang-Rice singlet band. Consistent with the changes in the spectral function, the optical conductivity shows a renormalization of the charge-transfer gap, which is proportional to the photodoping. The details of the photoinduced changes strongly depend on the dipolar matrix elements, which calls for an ab initio determination of these parameters.},
author = {Golez, Denis and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.100.235117},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2019-12-27},
peerreviewed = {Yes},
title = {{Multiband} nonequilibrium {GW}+{EDMFT} formalism for correlated insulators},
volume = {100},
year = {2019}
}
@article{faucris.240977890,
abstract = {The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green's functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract physically relevant information for the interpretation of experiments. We present the open-source software package NESSi (The Non-Equilibrium Systems Simulation package) which allows to perform many-body dynamics simulations based on Green's functions on the L-shaped Kadanoff–Baym contour. NESSi contains the library libcntr which implements tools for basic operations on these nonequilibrium Green's functions, for constructing Feynman diagrams, and for the solution of integral and integro-differential equations involving contour Green's functions. The library employs a discretization of the Kadanoff–Baym contour into time N points and a high-order implementation of integration routines. The total integrated error scales up to O(N^{−7}), which is important since the numerical effort increases at least cubically with the simulation time. A distributed-memory parallelization over reciprocal space allows large-scale simulations of lattice systems. We provide a collection of example programs ranging from dynamics in simple two-level systems to problems relevant in contemporary condensed matter physics, including Hubbard clusters and Hubbard or Holstein lattice models. The libcntr library is the basis of a follow-up software package for nonequilibrium dynamical mean-field theory calculations based on strong-coupling perturbative impurity solvers. Program summary: Program Title: NESSi CPC Library link to program files: http://dx.doi.org/10.17632/973crf9hgd.1 Licensing provisions: MPL v2.0 Programming language: C++, python External routines/libraries: cmake, eigen3, hdf5 (optional), mpi (optional), omp (optional) Nature of problem: Solves equations of motion of time-dependent Green's functions on the Kadanoff–Baym contour. Solution method: Higher-order solution methods of integral and integro-differential equations on the Kadanoff–Baym contour.},
author = {Schüler, Michael and Golež, Denis and Murakami, Yuta and Bittner, Nikolaj and Herrmann, Andreas and Strand, Hugo U.R. and Werner, Philipp and Eckstein, Martin},
doi = {10.1016/j.cpc.2020.107484},
faupublication = {yes},
journal = {Computer Physics Communications},
keywords = {Kadanoff–Baym equations; Keldysh formalism; Nonequilibrium dynamics of quantum many-body problems; Numerical simulations},
note = {CRIS-Team Scopus Importer:2020-07-31},
peerreviewed = {Yes},
title = {{NESSi}: {The} {Non}-{Equilibrium} {Systems} {Simulation} package},
volume = {257},
year = {2020}
}
@article{faucris.222104746,
abstract = {In time-resolved photoemission experiments, more than one electron can be emitted from the solid by a single ultrashort pulse. We theoretically demonstrate how correlations between the momenta of outgoing electrons relate to time-dependent two-particle correlations in the solid. This can extend the scope of time-and angle-resolved photoemission spectroscopy to probe superconducting and charge density fluctuations in systems without long-range order, and to reveal their dynamics independent of the electronic gap and thus unrestricted by the energy-time uncertainty. The proposal is illustrated for superconductivity in a BCS model. An impulsive perturbation can quench the gap on ultrafast timescales, while nonequilibrium pairing correlations persist much longer, even when electron-electron scattering beyond mean-field theory is taken into account. There is thus a clear distinction between a dephasing of the Cooper pairs and the thermalization into the normal state. While a measurement of the gap would be blind to such pairing correlations, they can be revealed by the angular correlations in photoemission.},
author = {Stahl, Christopher and Eckstein, Martin},
doi = {10.1103/PhysRevB.99.241111},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2019-07-12},
peerreviewed = {Yes},
title = {{Noise} correlations in time- and angle-resolved photoemission spectroscopy},
volume = {99},
year = {2019}
}
@article{faucris.258179433,
abstract = {Resonant inelastic X-ray scattering (RIXS) detects various types of high- and low-energy elementary excitations in correlated solids, and this tool will play an increasingly important role in investigations of time-dependent phenomena in photo-excited systems. While theoretical frameworks for the computation of equilibrium RIXS spectra are well established, the development of appropriate methods for nonequilibrium simulations is an active research field. Here, we apply a recently developed nonequilibrium dynamical mean field theory (DMFT) based approach to compute the RIXS response of photo-excited two-orbital Mott insulators. The results demonstrate the feasibility of multi-orbital nonequilibrium RIXS calculations and the sensitivity of the quasi-elastic fluorescence-like features and d-d excitation peaks on the nonequilibrium population of the Hubbard bands.},
author = {Werner, Philipp and Johnston, Steven and Eckstein, Martin},
doi = {10.1209/0295-5075/133/57005},
faupublication = {yes},
journal = {EPL - Europhysics Letters},
note = {CRIS-Team Scopus Importer:2021-05-14},
peerreviewed = {Yes},
title = {{Nonequilibrium}-{DMFT} based {RIXS} investigation of the two-orbital {Hubbard} model},
volume = {133},
year = {2021}
}
@article{faucris.267816536,
abstract = {The optical conductivity contains information about energy absorption and the underlying physical processes. In finite-dimensional systems, vertex corrections to the bare bubble need to be considered, which is a computationally challenging task. Recent numerical studies showed that in the weak-coupling limit, near an ordering instability with wave-vector pi, the vertical ladder describing particle-hole pairs interacting via the exchange of this wave vector becomes the dominant vertex correction. The corresponding Maki-Thompson-like diagram has been dubbed pi-ton. Here we add the pi-ton ladder vertex correction to dynamical mean-field theory estimates of the optical conductivity. By performing calculations on the Kadanoff-Baym contour, we reveal the characteristic spectral signatures of the pi-tons and their evolution under nonequilibrium conditions. We consider interaction quenches of the weakly correlated Hubbard model near the antiferromagnetic phase boundary and analyze the evolution of the Drude and pi-ton features. While the bubble contribution to the optical conductivity is found to thermalize rapidly, after some oscillations with frequencies related to the local spectral function, the pi-ton contribution exhibits a slower evolution. We link this observation to the prethermalization phenomenon which has been previously studied in weakly interacting, quenched Hubbard models.},
author = {Simard, Olivier and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.104.245127},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2022-01-07},
peerreviewed = {Yes},
title = {{Nonequilibrium} evolution of the optical conductivity of the weakly interacting {Hubbard} model: {Drude} response and pi-ton type vertex corrections},
volume = {104},
year = {2021}
}
@article{faucris.263728020,
abstract = {We use the nonequilibrium dynamical mean-field theory formalism to compute the equilibrium and nonequilibrium resonant inelastic x-ray scattering (RIXS) signal of a strongly interacting fermionic lattice model with a coupling of dispersionless phonons to the total charge on a given site. In the atomic limit, this model produces phonon subbands in the spectral function, but not in the RIXS signal. Electron hopping processes however result in phonon-related modifications of the charge excitation peak. We discuss the equilibrium RIXS spectra and the characteristic features of nonequilibrium states induced by photo-doping and by the application of a static electric field. The latter produces features related to Wannier-Stark states, which are dressed with phonon sidebands. Thanks to the effect of field-induced localization, the phonon features can be clearly resolved even in systems with weak electron-phonon coupling.},
author = {Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.104.085155},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-09-10},
peerreviewed = {Yes},
title = {{Nonequilibrium} resonant inelastic x-ray scattering study of an electron-phonon model},
volume = {104},
year = {2021}
}
@article{faucris.249334706,
abstract = {Photodoped states are widely observed in laser-excited Mott insulators, in which charge excitations are quickly created and can exist beyond the duration of the external driving. Despite the fruitful experimental explorations, theoretical studies on the microscopic models face the challenge to simultaneously deal with exponentially separated time scales, especially in multiband systems, where the longtime behaviors are often well beyond the reach of state-of-the-art numerical tools. Here, we address this difficulty by introducing a steady-state description of photodoped Mott insulators using an open-system setup, where the photodoped system is stabilized as a nonequilibrium steady state by a weak external driving. Taking advantage of the stationarity, we implement and discuss the details of an efficient numerical tool using the steady-state dynamical mean-field theory combined with the noncrossing approximation. We demonstrate that these stationary photodoped states exhibit the same properties of their transient counterparts, while being solvable with reasonable computational efforts. Furthermore, they can be parametrized by just a few physical quantities, including the effective temperature and the density of charge excitations, which confirms the universal nature of photodoped states indeed independent of the excitation protocols. As a first application, we consider the stationary photodoped states in a two-band Hubbard model with intertwined spin-and-orbital ordering and find a family of hidden phases unknown from the previous studies, implying an apparently unexplored time regime of the relaxation of the intertwined orders.},
author = {Li, Jiajun and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.045133},
faupublication = {yes},
journal = {Physical Review B},
month = {Jan},
note = {CRIS-Team Scopus Importer:2021-02-12},
peerreviewed = {Yes},
title = {{Nonequilibrium} steady-state theory of photodoped {Mott} insulators},
volume = {103},
year = {2021}
}
@article{faucris.265174821,
abstract = {We demonstrate that there exists a continuum Hamiltonian H(r, p) that is formally the operator equivalent of the general tight-binding method, inheriting the associativity and Hermiticity of the latter operator. This provides a powerful and controlled method of obtaining effective Hamiltonians via Taylor expansion with respect to momentum and, optionally, deformation fields. In particular, for fundamentally nonperturbative defects, such as twist faults and partial dislocations, the method allows the deformation field to be retained to all orders, providing an efficient scheme for the generation of transparent and compact Hamiltonians for such defects. We apply the method to a survey of incommensurate physics in twist bilayers of graphene, graphdiyne, MoS2, and phosphorene. For graphene we are able to reproduce the "reflected Dirac cones" of the 30 degrees quasicrystalline bilayer found in a recent angle-resolved photoemission spectroscopy experiment, and we show that it is an example of a more general phenomenon of coupling by the moire momentum. We show that incommensurate physics is governed by the decay of the interlayer interaction on the scale of the single-layer reciprocal lattices, and demonstrate that incommensurate scattering effects lead to a very rapid broadening of band manifolds as the twist angle is tuned through commensurate values.},
author = {Rost, Fabian and Gupta, R. and Fleischmann, Maximilian and Weckbecker, Dominik and Ray, Nicolas and Olivares, J. and Vogl, Michael and Sharma, S. and Pankratov, Oleg and Shallcross, Sam},
doi = {10.1103/PhysRevB.100.035101},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-10-18},
peerreviewed = {Yes},
title = {{Nonperturbative} theory of effective {Hamiltonians} for deformations in two-dimensional materials: {Moire} systems and dislocations},
volume = {100},
year = {2019}
}
@article{faucris.215695913,
abstract = {In order to have a better understanding of ultrafast electrical control of exchange interactions in multi-orbital systems, we study a two-orbital Hubbard model at half filling under the action of a time-periodic electric field. Using suitable projection operators and a generalized time-dependent canonical transformation, we derive an effective Hamiltonian which describes two different regimes. First, for a wide range of non-resonant frequencies, we find a change of the bilinear Heisenberg exchange J(ex) that is analogous to the single-orbital case. Moreover we demonstrate that also the additional biquadratic exchange interaction B-ex can be enhanced, reduced and even change sign depending on the electric field. Second, for special driving frequencies, we demonstrate a novel spin-charge coupling phenomenon enabling coherent transfer between spin and charge degrees of freedom of doubly ionized states. These results are confirmed by an exact time-evolution of the full two-orbital Mott-Hubbard Hamiltonian.},
author = {Barbeau, Marion M. S. and Eckstein, Martin and Katsnelson, Mikhail and Mentink, Johan H.},
doi = {10.21468/SciPostPhys.6.3.027},
faupublication = {yes},
journal = {SciPost Physics},
note = {CRIS-Team WoS Importer:2019-04-09},
peerreviewed = {Yes},
title = {{Optical} control of competing exchange interactions and coherent spin-charge coupling in two-orbital {Mott} insulators},
volume = {6},
year = {2019}
}
@article{faucris.233504578,
abstract = {Parallel ("nested") regions of a Fermi surface (FS) drive instabilities of the electron fluid, for example, the spin density wave in elemental chromium. In one-dimensional materials, the FS is trivially fully nested (a single nesting vector connects two "Fermi dots"), while in higher dimensions only a fraction of the FS consists of parallel sheets. We demonstrate that the tiny angle regime of twist bilayer graphene (TBLG) possesses a phase, accessible by interlayer bias, in which the FS consists entirely of nestable "Fermi lines", the first example of a completely nested FS in a two-dimensional (2D) material. This nested phase is found both in the ideal as well as relaxed structure of the twist bilayer. We demonstrate excellent agreement with recent STM images of topological states in this material and elucidate the connection between these and the underlying Fermiology. We show that the geometry of the Fermi lines network is controllable by the strength of the applied interlayer bias, and thus TBLG offers unprecedented access to the physics of FS nesting in 2D materials.},
author = {Fleischmann, Maximilian and Gupta, Reena and Wullschläger, Florian and Theil, Simon and Weckbecker, Dominik and Meded, Velimir and Sharma, Sangeeta and Meyer, Bernd and Shallcross, Sam},
doi = {10.1021/acs.nanolett.9b04027},
faupublication = {yes},
journal = {Nano Letters},
keywords = {Fermi surface nesting; Graphene; helical network; twist bilayer},
note = {CRIS-Team Scopus Importer:2020-02-07},
peerreviewed = {Yes},
title = {{Perfect} and {Controllable} {Nesting} in {Minimally} {Twisted} {Bilayer} {Graphene}},
year = {2020}
}
@article{faucris.117934784,
abstract = {Persistent conductivity in n-type 3C-SiC is investigated in a wide temperature range down to 3 K by Hall effect, admittance spectroscopy, low temperature photoluminescence (LTPL) and Raman spectroscopy. We propose a model, which clearly explains the persistent behavior of the electron density η below 50 K. It is experimentally verified that the persistent conductivity results from doped SF bunches, which can be considered nano-polytype inclusions in 3C-SiC. © (2014) Trans Tech Publications, Switzerland.},
author = {Beljakowa, Svetlana and Hauck, Martin and Bockstedte, Michel Georg and Fromm, Felix and Hundhausen, Martin and Nagasawa, H. and Weber, Heiko B. and Pensl, Gerhard and Krieger, Michael},
doi = {10.4028/www.scientific.net/MSF.778-780.265},
faupublication = {yes},
journal = {Materials Science Forum},
keywords = {3C-SiC; Hall effect; Persistent conductivity; Raman spectroscopy; Stacking faults (SFs)},
note = {UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.persis},
pages = {265-268},
peerreviewed = {Yes},
title = {{Persistent} {Conductivity} in n-type {3C}-{SiC} {Observed} at {Low} {Temperatures}},
volume = {778-780},
year = {2014}
}
@article{faucris.235413831,
abstract = {We investigate the effect of nonlocal interactions on the photodoped Mott insulating state of the two-dimensional Hubbard model using a nonequilibrium generalization of the dynamical cluster approximation. In particular, we compare the situation where the excitonic states are lying within the continuum of doublon-holon excitations to a setup where the excitons appear within the Mott gap. In the first case, the creation of nearest-neighbor doublon-holon pairs by excitations across the Mott gap results in enhanced excitonic correlations, but these excitons quickly decay into uncorrelated doublons and holons. In the second case, photoexcitation results in long-lived excitonic states. While in a low-temperature equilibrium state, excitonic features are usually not evident in single-particle observables such as the photoemission spectrum, we show that the photoexcited nonequilibrium system can exhibit in-gap states associated with the excitons. The comparison with exact-diagonalization results for small clusters allows us to identify the signatures of the excitons in the photoemission spectrum.},
author = {Bittner, Nikolaj and Golež, Denis and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.101.085127},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2020-03-06},
peerreviewed = {Yes},
title = {{Photoenhanced} excitonic correlations in a {Mott} insulator with nonlocal interactions},
volume = {101},
year = {2020}
}
@article{faucris.259922351,
abstract = {Photodoping of Mott insulators or correlated metals can create an unusual metallic state which simultaneously hosts holelike and electronlike particles. We study the dynamics of this state up to long times, as it passes its kinetic energy to the environment. When the system cools down, it crosses over from a bad metal into a resilient quasiparticle regime, in which quasiparticle bands are formed with separate Fermi levels for electrons and holes, but quasiparticles do not yet satisfy the Fermi-liquid paradigm. Subsequently, the transfer of energy to the environment slows down significantly, and the system does not reach the Fermi-liquid state even on the timescale of picoseconds. The transient photodoped strange metal exhibits unusual properties of relevance for ultrafast charge and heat transport: In particular, there can be an asymmetry in the properties of electrons and holes, and strong correlations between electrons and holes, as seen in the spectral properties.},
author = {Dasari, Nagamalleswara Rao and Li, Jiajun and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.L201116},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-06-11},
peerreviewed = {Yes},
title = {{Photoinduced} strange metal with electron and hole quasiparticles},
volume = {103},
year = {2021}
}
@article{faucris.201672046,
abstract = {We show that, in optical pump-probe experiments on bulk samples, the statistical distribution of the intensity of ultrashort light pulses after interaction with a nonequilibrium complex material can be used to measure the time-dependent noise of the current in the system. We illustrate the general arguments for a photoexcited Peierls material. The transient noise spectroscopy allows us to measure to what extent electronic degrees of freedom dynamically obey the fluctuation-dissipation theorem, and how well they thermalize during the coherent lattice vibrations. The proposed statistical measurement developed here provides a new general framework to retrieve dynamical information on the excited distributions in nonequilibrium experiments, which could be extended to other degrees of freedom of magnetic or vibrational origin.},
author = {Randi, Francesco and Esposito, Martina and Giusti, Francesca and Misochko, Oleg and Parmigiani, Fulvio and Fausti, Daniele and Eckstein, Martin},
doi = {10.1103/PhysRevLett.119.187403},
faupublication = {no},
journal = {Physical Review Letters},
peerreviewed = {Yes},
title = {{Probing} the {Fluctuations} of {Optical} {Properties} in {Time}-{Resolved} {Spectroscopy}},
volume = {119},
year = {2017}
}
@article{faucris.281166946,
abstract = {We present a quantum impurity solver based on a pseudoparticle framework, which combines diagrammatic resummations for a three-point vertex with diagrammatic Monte Carlo sampling of a four-point vertex. This recently proposed approach (A. J. Kim, arXiv:2112.15549) is generalized here to fermionic impurity problems and we discuss the technical details of the implementation, including the time-stepping approach, the Monte Carlo updates, and the routines for checking the two-particle irreducibility of the four-point vertex. We also explain how the vertex information can be efficiently stored using a Dubiner basis representation. The convergence properties of the algorithm are demonstrated with applications to exactly solvable impurity models and dynamical mean field theory simulations of the single-orbital Hubbard model. It is furthermore shown that the algorithm can handle a two-orbital problem with off-diagonal hybridizations, which would cause a severe sign problem in standard hybridization-expansion Monte Carlo simulations. Since the vertex-based algorithm successfully handles sign-oscillating integrals in equilibrium and samples only connected diagrams, it may be a promising approach for real-time simulations.},
author = {Kim, Aaram J. and Li, Jiajun and Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.106.085124},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2022-09-02},
peerreviewed = {Yes},
title = {{Pseudoparticle} vertex solver for quantum impurity models},
volume = {106},
year = {2022}
}
@article{faucris.262967217,
abstract = {Collective orders and photoinduced phase transitions in quantum matter can evolve on timescales which are orders of magnitude slower than the femtosecond processes related to electronic motion in the solid. Quantum Boltzmann equations can potentially resolve this separation of timescales, but are often constructed by assuming the existence of quasiparticles. Here we derive a quantum Boltzmann equation which only assumes a separation of timescales (taken into account through the gradient approximation for convolutions in time), but is based on a nonperturbative scattering integral, and makes no assumption on the spectral function such as the quasiparticle approximation. In particular, a scattering integral corresponding to nonequilibrium dynamical mean-field theory is evaluated in terms of an Anderson impurity model in a nonequilibrium steady state with prescribed distribution functions. This opens the possibility to investigate dynamical processes in correlated solids with quantum impurity solvers designed for the study of nonequilibrium steady states.},
author = {Picano, Antonio and Li, Jiajun and Eckstein, Martin},
doi = {10.1103/PhysRevB.104.085108},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-08-20},
peerreviewed = {Yes},
title = {{Quantum} {Boltzmann} equation for strongly correlated electrons},
volume = {104},
year = {2021}
}
@article{faucris.229589749,
abstract = {We perform an ab initio comparison between nonequilibrium dynamical mean-field theory and optical lattice experiments by studying the time evolution of double occupations in the periodically driven Fermi-Hubbard model. For off-resonant driving, the range of validity of a description in terms of an effective static Hamiltonian is determined and its breakdown due to energy absorption close to resonance is demonstrated. For near-resonant driving, we investigate the response to a change in driving amplitude and discover an asymmetric excitation spectrum with respect to the detuning. In general, we find good agreement between experiment and theory, which cross validates the experimental and numerical approaches in a strongly correlated nonequilibrium system.},
author = {Sandholzer, Kilian and Murakami, Yuta and Görg, Frederik and Minguzzi, Joaquín and Messer, Michael and Desbuquois, Rémi and Eckstein, Martin and Werner, Philipp and Esslinger, Tilman},
doi = {10.1103/PhysRevLett.123.193602},
faupublication = {yes},
journal = {Physical Review Letters},
note = {CRIS-Team Scopus Importer:2019-11-22},
peerreviewed = {Yes},
title = {{Quantum} {Simulation} {Meets} {Nonequilibrium} {Dynamical} {Mean}-{Field} {Theory}: {Exploring} the {Periodically} {Driven}, {Strongly} {Correlated} {Fermi}-{Hubbard} {Model}},
volume = {123},
year = {2019}
}
@article{faucris.248099002,
abstract = {Light-matter coupling involving classical and quantum light offers a wide range of possibilities to tune the electronic properties of correlated quantum materials. Two paradigmatic results are the dynamical localization of electrons and the ultrafast control of spin dynamics, which have been discussed within classical Floquet engineering and in the deep quantum regime where vacuum fluctuations modify the properties of materials. Here we discuss how these two extreme limits are interpolated by a cavity which is driven to the excited states. In particular, this is achieved by formulating a Schrieffer-Wolff transformation for the cavity-coupled system, which is mathematically analogous to its Floquet counterpart. Some of the extraordinary results of Floquet engineering, such as the sign reversal of the exchange interaction or electronic tunneling, which are not obtained by coupling to a dark cavity, can already be realized with a single-photon state (no coherent states are needed). The analytic results are verified and extended with numerical simulations on a two-site Hubbard model coupled to a driven cavity mode. Our results generalize the well-established Floquet engineering of correlated electrons to the regime of quantum light. This opens up a pathway of controlling properties of quantum materials with high tunability and low energy dissipation.},
author = {Sentef, Michael A. and Li, Jiajun and Künzel, Fabian and Eckstein, Martin},
doi = {10.1103/PhysRevResearch.2.033033},
faupublication = {yes},
journal = {Physical Review Research},
note = {CRIS-Team WoS Importer:2021-01-22},
peerreviewed = {Yes},
title = {{Quantum} to classical crossover of {Floquet} engineering in correlated quantum systems},
volume = {2},
year = {2020}
}
@article{faucris.237703332,
abstract = {We investigate the strong-field dynamics of a paramagnetic two-band Mott insulator using real-time dynamical mean-field theory. We demonstrate that strong electric fields can lead to a transient localization of electrons. This nonequilibrium quantum effect allows us to reveal specific signatures of local correlations in the time-resolved photoemission spectrum. In particular, we demonstrate that the localization can be strong enough to produce atomiclike spin multiplets determined by the Hund's coupling J, and thus provide a way of measuring J inside the solid. Our simulation also fully incorporates nonlinear field-induced tunneling processes, which would lead to a dielectric breakdown in the steady state limit. A careful analysis of these processes, however, shows that they remain weak enough and do not prevent the measurement of the transiently localized spectra.},
author = {Dasari, Nagamalleswara Rao and Li, Jiajun and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.101.161107},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2020-04-24},
peerreviewed = {Yes},
title = {{Revealing} {Hund}'s multiplets in {Mott} insulators under strong electric fields},
volume = {101},
year = {2020}
}
@article{faucris.255354585,
abstract = {We develop a framework to evaluate the time-dependent resonant inelastic x-ray scattering (RIXS) signal with the use of nonequilibrium dynamical mean-field theory simulations. The approach is based on the solution of a time-dependent impurity model which explicitly incorporates the probe pulse. It avoids the need to compute four-point correlation functions and can in principle be combined with different impurity solvers. This opens a path to study time-resolved RIXS processes in multiorbital systems. The approach is exemplified with a study of the RIXS signal of a melting Mott antiferromagnet.},
author = {Eckstein, Martin and Werner, Philipp},
doi = {10.1103/PhysRevB.103.115136},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2021-04-16},
peerreviewed = {Yes},
title = {{Simulation} of time-dependent resonant inelastic x-ray scattering using nonequilibrium dynamical mean-field theory},
volume = {103},
year = {2021}
}
@article{faucris.308581712,
abstract = {We discuss a semiclassical approach to solve the quantum impurity model within nonequilibrium dynamical mean-field theory for electron-lattice models. The effect of electronic fluctuations on the phonon is kept beyond Ehrenfest dynamics, leading to a stochastic phonon evolution with damping and noise terms that are self-consistently determined by the electronic correlation functions in the fluctuating phonon field. Together with a solution of the electronic model based on a nonperturbative quantum Boltzmann equation, the approach can be used to address the coupled dynamics of the electrons and the lattice during photoinduced phase transitions. Results for the Anderson-Holstein model are benchmarked against numerically exact quantum Monte Carlo data. We find good agreement for the phonon distribution function at temperatures comparable to the charge ordering temperature. The general formulation can be extended to models with electron-electron interactions or multiorbital systems.},
author = {Picano, Antonio and Grandi, Francesco and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevB.108.035115},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2023-08-04},
peerreviewed = {Yes},
title = {{Stochastic} semiclassical theory for nonequilibrium electron-phonon coupled systems},
volume = {108},
year = {2023}
}
@article{faucris.265178782,
abstract = {We present a continuum theory of graphene, treating on an equal footing both the homogeneous Cauchy-Born (CB) deformation and the microscopic degrees of freedom associated with the two sublattices. While our theory recovers all extant results from homogeneous continuum theory, the Dirac-Weyl equation is found to be augmented by new pseudogauge and chiral fields fundamentally different from those that result from homogeneous deformation. We elucidate three striking electronic consequences: (i) non-CB deformations allow for the transport of valley-polarized charge over arbitrarily long distances, e.g., along a designed ridge; (ii) the triaxial deformations required to generate an approximately uniform magnetic field are unnecessary with non-CB deformation; and finally (iii) the vanishing of the effects of a one-dimensional corrugation seen in ab initio calculation upon lattice relaxation is explained as a compensation of CB and non-CB deformation.},
author = {Gupta, Reena and Rost, Fabian and Fleischmann, Maximilian and Sharma, S. and Shallcross, Sam},
doi = {10.1103/PhysRevB.99.125407},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-10-18},
peerreviewed = {Yes},
title = {{Straintronics} beyond homogeneous deformation},
volume = {99},
year = {2019}
}
@article{faucris.240319596,
abstract = {Ultrafast laser pulses can redistribute charges in Mott insulators on extremely short time scales, leading to the fast generation of photocarriers. It has recently been demonstrated that these photocarriers can form a novel η-paired condensate at low temperatures, featuring a staggered superconducting pairing field. In this conference paper, we discuss the origin of the η-paired hidden phase and its optical response, which may be detected in a pump-probe experiment. The hidden phase may be relevant for possible light-induced superconductivity in Mott insulators.},
author = {Li, Jiajun and Golez, D. and Werner, P. and Eckstein, Martin},
doi = {10.1142/S0217984920400540},
faupublication = {yes},
journal = {Modern Physics Letters B},
keywords = {Mott insulators; photocarriers; Superconducting optical response; ultrafast laser techniques},
note = {CRIS-Team Scopus Importer:2020-07-10},
peerreviewed = {Yes},
title = {{Superconducting} optical response of photodoped {Mott} insulators},
year = {2020}
}
@article{faucris.328577937,
abstract = {Field emission is a powerful technique to gain insight into the electronic properties of materials. A strong and ultrashort laser pulse can periodically modify the potential barrier for electron tunnelling, giving rise to photon sidebands in the far-field electron energy distribution. The aim of this work is to present a novel tight-binding approach that simulates the laser-assisted field emission from a metallic tip taking account also of the electronic features of the emitter. The out-of-equilibrium electron dynamics of this inhomogeneous system is described using the Green's function formalism.},
author = {D'Onofrio, L. J. and Avella, A. and Eckstein, Martin},
doi = {10.1393/ncc/i2024-24292-7},
faupublication = {yes},
journal = {Il Nuovo Cimento C - Colloquia on Physics},
note = {CRIS-Team Scopus Importer:2024-09-13},
peerreviewed = {Yes},
title = {{Tight}-binding simulation of ultrafast pulse-assisted field emission from a metallic tip},
volume = {47},
year = {2024}
}
@article{faucris.289296436,
abstract = {Inspired by the physics of rare-earth nickelates, we study the photoemission (PES) and resonant inelastic x-ray scattering (RIXS) spectra of a correlated electron system with two types of insulating sublattices. Sublattice A is characterized by a hybridization gap and a low-spin state, while sublattice B features a Mott gap and a local magnetic moment. We show how the coupling of these two qualitatively different insulating states affects the dynamics of photoinduced charge carriers and how the nonequilibrium states manifest themselves in the PES and RIXS signals. In particular, we find that charge carriers created on the B sublattice migrate to the A sublattice, where they contribute to the creation of in-gap states in the PES signal and to characteristic peaks in the nonequilibrium RIXS spectrum. While the contributions from the two sublattices cannot be easily distinguished in the local photoemission spectrum, the weights of the RIXS signals in the two-dimensional ωin-ωout space provide information on the local state evolution on both sublattices. },
author = {Werner, Philipp and Petocchi, Francesco and Eckstein, Martin},
doi = {10.1103/PhysRevB.107.035157},
faupublication = {yes},
journal = {Physical Review B},
month = {Jan},
note = {CRIS-Team Scopus Importer:2023-02-17},
peerreviewed = {Yes},
title = {{Time}-resolved photoemission and resonant inelastic x-ray scattering study of a site-selective {Mott} insulator},
volume = {107},
year = {2023}
}
@article{faucris.265784107,
abstract = {Time- and angular-resolved photoemission spectroscopy (trARPES) can directly probe the electronic structure of quantum materials out of equilibrium. This can shed light on the interaction of the electrons with spin, lattice, and orbital degrees of freedom, and help to unravel pathways towards novel out-of-equilibrium phases. Dynamical mean-field theory (DMFT) and its extensions provide a versatile toolbox to interpret such experiments through a theoretical simulation of the underlying microscopic processes. The approach can be applied both to Mott insulators and correlated metals, and it is formulated in terms of non-equilibrium Green's functions, which directly relate to the photoemission spectrum. This article reviews the theoretical description of trARPES within DMFT and related diagrammatic non-equilibrium Green's function techniques. Several applications are discussed, including the photo-induced melting of excitonic order, femtosecond relaxation processes in Mott insulators, and the manipulation of the electronic structure of Mott and charge transfer insulators using photodoping and strong THz fields.},
author = {Eckstein, Martin},
doi = {10.1016/j.elspec.2021.147108},
faupublication = {yes},
journal = {Journal of Electron Spectroscopy and Related Phenomena},
note = {CRIS-Team WoS Importer:2021-11-05},
peerreviewed = {Yes},
title = {{Time}-resolved photoemission spectroscopy on correlated electrons: {Insights} from dynamical mean-field theory},
volume = {253},
year = {2021}
}
@article{faucris.265178281,
abstract = {Deploying an analytical atomistic model of the bulk band structure of the IV-VI crystalline topological insulators, we connect the spin structure of the surface state to the crystal field and spin-orbit coupling parameters of the bulk material. While the Dirac-Weyl-type topological surface state is often assumed to be universal, we show that the physics of the surface state is strikingly nonuniversal, carrying a profound imprint of the bulk physics. To see this explicitly we calculate the Ruderman-Kittel-Kasuya-Yosida interaction, which may be viewed as a probe of this surface state spin structure, finding that its qualitative form depends on the values the bulk spin-orbit and crystal field parameters take. This opens the way to tune the spin interaction on the surface of a IV-VI topological insulator by, for instance, varying the composition of the IV-VI ternary compounds.},
author = {Klier, Nicolas and Sharma, S. and Rost, Fabian and Pankratov, Oleg and Shallcross, Sam},
doi = {10.1103/PhysRevB.100.075130},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2021-10-18},
peerreviewed = {Yes},
title = {{Tuning} topological surface magnetism by bulk alloying},
volume = {100},
year = {2019}
}
@article{faucris.282833362,
abstract = {Quasi-one-dimensional systems exhibit many-body effects elusive in higher dimensions. A prime example is spin-orbital separation, which has been measured by resonant inelastic x-ray scattering (RIXS) in Sr2CuO3. Here, we theoretically analyze the time-resolved RIXS spectrum of Sr2CuO3 under the action of a time-dependent electric field. We show that the external field can reversibly modify the parameters in the effective t-J model used to describe spinon and orbiton dynamics in the material. For strong driving amplitudes, we find that the spectrum changes qualitatively as a result of reversing the relative spinon to orbiton velocity. The analysis shows that in general, the spin-orbital dynamics in Mott insulators in combination with time-resolved RIXS should provide a suitable platform to explore the reversible control of many-body physics in the solid with strong laser fields. },
author = {Müller, Aaron and Grandi, Francesco and Eckstein, Martin},
doi = {10.1103/PhysRevB.106.L121107},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team Scopus Importer:2022-10-07},
peerreviewed = {Yes},
title = {{Ultrafast} control of spin-orbital separation probed with time-resolved resonant inelastic x-ray scattering},
volume = {106},
year = {2022}
}
@article{faucris.228038484,
abstract = {Highly intense electric field pulses can move the electronic momentum occupation in correlated metals over large portions of the Brillouin zone, leading to phenomena such as dynamic Bloch oscillations. Using the nonequilibrium fluctuation-exchange approximation for the two-dimensional Hubbard model, we study how such nonthermal electron distributions drive collective spin and charge fluctuations. Suitable pulses can induce a highly anisotropic modification of the occupied momenta, and the corresponding spin dynamics results in a transient change from antiferromagnetic to anisotropic ferromagnetic correlations. To good approximation this behavior is understood in terms of an instantaneous response of the spin correlations to the single-particle properties.},
author = {Dasari, Nagamalleswara Rao and Eckstein, Martin},
doi = {10.1103/PhysRevB.100.121114},
faupublication = {yes},
journal = {Physical Review B},
note = {CRIS-Team WoS Importer:2019-10-18},
peerreviewed = {Yes},
title = {{Ultrafast} electric field controlled spin correlations in the {Hubbard} model},
volume = {100},
year = {2019}
}
@article{faucris.249334956,
abstract = {Nonlinear phononics holds the promise for controlling properties of quantum materials on the ultrashort timescale. Using nonequilibrium dynamical mean-field theory, we solve a model for the description of organic solids, where correlated electrons couple nonlinearly to a quantum phonon mode. Unlike previous works, we exactly diagonalize the local phonon mode within the noncrossing approximation to include the full phononic fluctuations. By exciting the local phonon in a broad range of frequencies near resonance with an ultrashort pulse, we show it is possible to induce a Mott insulator-to-metal phase transition. Conventional semiclassical and mean-field calculations, where the electron-phonon interaction decouples, underestimate the onset of the quasiparticle peak. This fact, together with the nonthermal character of the photoinduced metal, suggests a leading role of the phononic fluctuations and of the dynamic nature of the state in the vibrationally induced quasiparticle coherence.},
author = {Grandi, Francesco and Li, Jiajun and Eckstein, Martin},
doi = {10.1103/PhysRevB.103.L041110},
faupublication = {yes},
journal = {Physical Review B},
month = {Jan},
note = {CRIS-Team Scopus Importer:2021-02-12},
peerreviewed = {Yes},
title = {{Ultrafast} {Mott} transition driven by nonlinear electron-phonon interaction},
volume = {103},
year = {2021}
}
@article{faucris.219419213,
abstract = {Ultrafast photodoping of the Mott insulators, possessing strong correlation between electronic and magnetic degrees of freedom, holds promise for launching an ultrafast dynamics of spins which cannot be described in terms of conventional models of ultrafast magnetism. Here we study the ultrafast laser-induced dynamics of the magnetic order in a novel spin-orbit Mott insulator Sr2IrO4 featuring an uncompensated pattern of antiferromagnetic spin ordering. Using the transient magneto-optical Kerr effect sensitive to the net magnetization, we reveal that photodoping by femtosecond laser pulses with photon energy above the Mott gap launches melting of the antiferromagnetic order seen as ultrafast demagnetization with a characteristic time of 300 fs followed by a sub-10-ps recovery. Nonequilibrium dynamical mean-field theory calculations based on the single-band Hubbard model confirm that ultrafast demagnetization is primarily governed by the laser-induced generation of electron-hole pairs, although the precise simulated time dependencies are rather different from the experimentally observed ones. To describe the experimental results, here we suggest a phenomenological model which is based on Onsager's formalism and accounts for the photogenerated electron-hole pairs using the concepts of holons and doublons.},
author = {Afanasiev, D. and Gatilova, A. and Groenendijk, D. J. and Ivanov, B. A. and Gibert, M. and Gariglio, S. and Mentink, J. and Li, Jiajun and Dasari, Nagamalleswara Rao and Eckstein, Martin and Rasing, Th. and Caviglia, A. D. and Kimel, A. V.},
doi = {10.1103/PhysRevX.9.021020},
faupublication = {yes},
journal = {Physical Review X},
note = {CRIS-Team WoS Importer:2019-06-04},
peerreviewed = {Yes},
title = {{Ultrafast} {Spin} {Dynamics} in {Photodoped} {Spin}-{Orbit} {Mott} {Insulator} {Sr2IrO4}},
volume = {9},
year = {2019}
}
@article{faucris.248104472,
abstract = {Vanadium dioxide is one of the most studied strongly correlated materials. Nonetheless, the intertwining between electronic correlation and lattice effects has precluded a comprehensive description of the rutile metal to monoclinic insulator transition, in turn triggering a longstanding "the chicken or the egg" debate about which comes first, the Mott localization or the Peierls distortion. Here, we suggest that this problem is in fact ill posed: The electronic correlations and the lattice vibrations conspire to stabilize the monoclinic insulator, and so they must be both considered to not miss relevant pieces of the VO2 physics. Specifically, we design a minimal model for VO2 that includes all the important physical ingredients: the electronic correlations, the multiorbital character, and the two components of the antiferrodistortive mode that condense in the monoclinic insulator. We solve this model by dynamical mean-field theory within the adiabatic Born-Oppenheimer approximation. Consistently with the first-order character of the metal-insulator transition, the Born-Oppenheimer potential has a rich landscape, with minima corresponding to the undistorted phase and to the four equivalent distorted ones, and which translates into an equally rich thermodynamics that we uncover by the Monte Carlo method. Remarkably, we find that a distorted metal phase intrudes between the low-temperature distorted insulator and high-temperature undistorted metal, which sheds new light on the debated experimental evidence of a monoclinic metallic phase.},
author = {Grandi, Francesco and Amaricci, Adriano and Fabrizio, M.},
doi = {10.1103/PhysRevResearch.2.013298},
faupublication = {yes},
journal = {Physical Review Research},
note = {CRIS-Team WoS Importer:2021-01-22},
peerreviewed = {Yes},
title = {{Unraveling} the {Mott}-{Peierls} intrigue in vanadium dioxide},
volume = {2},
year = {2020}
}
@article{faucris.289028020,
abstract = {We propose a diagrammatic Monte Carlo approach for quantum impurity models, which can be regarded as a generalization of the strong-coupling expansion for fermionic impurity models. The algorithm is based on a self-consistently computed three-point vertex and a stochastically sampled four-point vertex, and it allows one to obtain numerically exact results in a wide parameter regime. The performance of the algorithm is demonstrated with applications to a spin-boson model representing an emitter in a waveguide. As a function of the coupling strength, the spin exhibits a delocalization-localization crossover at low temperatures, signaling a qualitative change in the real-time relaxation. In certain parameter regimes, the response functions of the emitter coupled to the electromagnetic continuum can be described by an effective Rabi model with appropriately defined parameters. We also discuss the spatial distribution of the photon density around the emitter.},
author = {Kim, Aaram J. and Lenk, Katharina and Li, Jiajun and Werner, Philipp and Eckstein, Martin},
doi = {10.1103/PhysRevLett.130.036901},
faupublication = {yes},
journal = {Physical Review Letters},
month = {Jan},
note = {CRIS-Team Scopus Importer:2023-02-10},
peerreviewed = {Yes},
title = {{Vertex}-{Based} {Diagrammatic} {Treatment} of {Light}-{Matter}-{Coupled} {Systems}},
volume = {130},
year = {2023}
}
@article{faucris.110717904,
abstract = {We investigate the role of electronic-vibrational coupling in resonant electron transport through single-molecule junctions, taking into account that the corresponding coupling strengths may depend on the charge and excitation state of the molecular bridge. Within an effective-model Hamiltonian approach for a molecule with multiple electronic states, this requires to extend the commonly used model and include vibrationally dependent electron-electron interaction. We use Born-Markov master equation methods and consider selected models to exemplify the effect of the additional interaction on the transport characteristics of a single-molecule junction. In particular, we show that it has a significant influence on local cooling and heating mechanisms, it may result in negative differential resistance, and it may cause pronounced asymmetries in the conductance map of a single-molecule junction.},
author = {Erpenbeck, André and Haertle, R. and Bockstedte, Michel Georg and Thoss, Michael},
doi = {10.1103/PhysRevB.93.115421},
faupublication = {yes},
journal = {Physical Review B},
note = {UnivIS-Import:2017-12-18:Pub.2016.nat.dphy.ITP.ppem.vibrat},
pages = {115421},
peerreviewed = {Yes},
title = {{Vibrationally} dependent electron-electron interactions in resonant electron transport through single-molecule junctions},
url = {http://link.aps.org/doi/10.1103/PhysRevB.93.115421},
volume = {93},
year = {2016}
}