Correlated electron systems periodically driven out of equilibrium: Floquet + DMFT formalism

TL;DR

This paper introduces a combined Floquet and DMFT approach to study strongly correlated electron systems under periodic driving, enabling nonperturbative analysis of photoinduced phase transitions.

Contribution

It develops a novel formalism integrating Floquet theory with DMFT to analyze nonlinear, out-of-equilibrium effects in correlated electrons under intense ac fields.

Findings

Photoinduced midgap states emerge under strong ac fields.

The method accurately captures insulator-metal transitions.

Spectral functions reveal nonlinear effects of driving fields.

Abstract

We propose to combine the Floquet formalism for systems in ac fields with the dynamical mean-field theory to study correlated electron systems periodically driven out of equilibrium by external fields such as intense laser light. This approach has a virtue that we can nonperturbatively include both the correlation effects and nonlinear effects due to the driving field, which is imperative in analyzing recent experiments for photoinduced phase transitions. In solving the problem, we exploit a general theorem that the Hamiltonian in a Floquet matrix form can be exactly diagonalized for single-band noninteracting systems. As a demonstration, we have applied the method to the Falicov-Kimball model in intense ac fields to calculate the spectral function. The result shows that photoinduced midgap states emerge from strong ac fields, triggering an insulator-metal transition.