Université de Fribourg

Nonequilibrium steady states and transient dynamics of conventional superconductors under phonon driving

Murakami, Yuta ; Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 4, p. 045125

We perform a systematic analysis of the influence of phonon driving on the superconducting Holstein model coupled to heat baths by studying both the transient dynamics and the nonequilibrium steady state (NESS) in the weak and strong electron-phonon coupling regimes. Our study is based on the nonequilibrium dynamical mean-field theory, and for the NESS we present a Floquet formulation ...

Université de Fribourg

Exact out-of-time-ordered correlation functions for an interacting lattice fermion model

Tsuji, Naoto ; Werner, Philipp ; Ueda, Masahito

In: Physical Review A, 2017, vol. 95, no. 1, p. 011601

Exact solutions for local equilibrium and nonequilibrium out-of-time-ordered correlation (OTOC) functions are obtained for a lattice fermion model with on-site interactions, namely, the Falicov-Kimball (FK) model, in the large dimensional and thermodynamic limit. Our approach is based on the nonequilibrium dynamical mean-field theory generalized to an extended Kadanoff-Baym contour. We find...

Université de Fribourg

Nonequilibrium dynamical cluster approximation study of the Falicov-Kimball model

Herrmann, Andreas J. ; Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2016, vol. 94, no. 24, p. 245114

We use a nonequilibrium implementation of the dynamical cluster approximation (DCA) to study the effect of short-range correlations on the dynamics of the two-dimensional Falicov-Kimball model after an interaction quench. As in the case of single-site dynamical mean-field theory, thermalization is absent in DCA simulations, and for quenches across the metal-insulator boundary,...

Université de Fribourg

Damping of the collective amplitude mode in superconductors with strong electron-phonon coupling

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2016, vol. 94, no. 11, p. 115126

We study the effect of strong electron-phonon interactions on the damping of the Higgs amplitude mode in superconductors by means of nonequilibrium dynamical mean-field simulations of the Holstein model. In contrast to the BCS dynamics, we find that the damping of the Higgs mode strongly depends on the temperature, becoming faster as the system approaches the transition temperature. The...

Université de Fribourg

Multiple amplitude modes in strongly coupled phonon-mediated superconductors

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2016, vol. 93, no. 9, p. 94509

We study collective amplitude modes of the superconducting order parameter in strongly coupled electron-phonon systems described by the Holstein model using the nonequilibrium dynamical mean-field theory with the self-consistent Migdal approximation as an impurity solver. The frequency of the Higgs amplitude mode is found to coincide with the superconducting gap even in the strongly coupled...

Université de Fribourg

Interaction quench in the Holstein model: Thermalization crossover from electron- to phonon-dominated relaxation

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2015, vol. 91, no. 4, p. 045128

We study the relaxation of the Holstein model after a sudden switch-on of the interaction by means of the nonequilibrium dynamical mean field theory, with the self-consistent Migdal approximation as an impurity solver. We show that there exists a qualitative change in the thermalization dynamics as the interaction is varied in the weak-coupling regime. On the weaker interaction side of this...

Université de Fribourg

Nonequilibrium dynamical mean-field theory and its applications

Aoki, Hideo ; Tsuji, Naoto ; Eckstein, Martin ; Kollar, Marcus ; Oka, Takashi ; Werner, Philipp

In: Reviews of Modern Physics, 2014, vol. 86, no. 2, p. 779–837

The study of nonequilibrium phenomena in correlated lattice systems has developed into one of the most active and exciting branches of condensed matter physics. This research field provides rich new insights that could not be obtained from the study of equilibrium situations, and the theoretical understanding of the physics often requires the development of new concepts and methods. On the...

Université de Fribourg

Ordered phases in the Holstein-Hubbard model: Interplay of strong Coulomb interaction and electron-phonon coupling

Murakami, Yuta ; Werner, Philipp ; Tsuji, Naoto ; Aoki, Hideo

In: Physical Review B, 2013, vol. 88, no. 12, p. 125126

We study the Holstein-Hubbard model at half filling to explore ordered phases including superconductivity (SC), antiferromagnetism (AF), and charge order (CO) in situations where the electron-electron and electron-phonon interactions are strong (comparable to the electronic bandwidth). The model is solved in the dynamical mean-field approximation with a continuous-time quantum Monte Carlo...

Université de Fribourg

Nonequilibrium dynamical mean-field theory based on weak-coupling perturbation expansions: Application to dynamical symmetry breaking in the Hubbard model

Tsuji, Naoto ; Werner, Philipp

In: Physical Review B, 2013, vol. 88, no. 16, p. 165115

We discuss the general formalism and validity of weak-coupling perturbation theory as an impurity solver for nonequilibrium dynamical mean-field theory. The method is implemented and tested in the Hubbard model, using expansions up to fourth order for the paramagnetic phase at half filling and third order for the antiferromagnetic and paramagnetic phase away from half filling. We explore various...

Université de Fribourg

Nonthermal Antiferromagnetic Order and Nonequilibrium Criticality in the Hubbard Model

Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2013, vol. 110, no. 13, p. 136404

We study dynamical phase transitions from antiferromagnetic to paramagnetic states driven by an interaction quench in the fermionic Hubbard model using the nonequilibrium dynamical mean-field theory. We identify two dynamical transition points where the relaxation behavior qualitatively changes: one corresponds to the thermal phase transition at which the order parameter decays critically slowly...