A comparative study of nonequilibrium insulator-to-metal transitions in electron-phonon systems

TL;DR

This paper investigates how electron-phonon interactions induce insulator-to-metal transitions in the Hubbard-Holstein model, comparing theoretical methods and revealing transient non-thermal metallic states post-quench.

Contribution

It provides a comparative analysis of impurity solvers and uncovers the existence of transient metallic states under nonequilibrium conditions.

Findings

Slave-rotor method indicates a critical coupling for non-thermal metallic trapping.

One-crossing approximation shows a bad metallic state after quench.

Benchmarking against NRG validates the impurity solvers' equilibrium results.

Abstract

We study equilibrium and nonequilibrium properties of electron-phonon systems described by the Hubbard-Holstein model using the dynamical mean-field theory. In equilibrium, we benchmark the results for impurity solvers based on the one-crossing approximation and slave-rotor approximation against non-perturbative numerical renormalization group reference data. We also examine how well the low energy properties of the electron-boson coupled systems can be reproduced by an effective static electron-electron interaction. The one-crossing and slave-rotor approximations are then used to simulate insulator-to-metal transitions induced by a sudden switch-on of the electron-phonon interaction. The slave-rotor results suggest the existence of a critical electron-phonon coupling above which the system is transiently trapped in a non-thermal metallic state with coherent quasiparticles. The same quench protocol in the one-crossing approximation results in a bad metallic state.