Floquet dynamics in light-driven solids

TL;DR

This paper develops a framework to understand how light-driven Floquet states in solids influence physical observables like Hall conductivity, incorporating environmental dissipation effects to match experimental results.

Contribution

It introduces a dissipative Floquet theory framework that accounts for environmental effects, providing a realistic interpretation of light-induced phenomena in solids.

Findings

Good quantitative agreement with experimental Hall conductivity data

Floquet states' occupations are determined by a balance of optical driving and dissipation

Hall conductivity can be interpreted as a geometric-dissipative effect

Abstract

We demonstrate how the properties of light-induced electronic Floquet states in solids impact natural physical observables, such as transport properties, by capturing the environmental influence on the electrons. We include the environment as dissipative processes, such as inter-band decay and dephasing, often ignored in Floquet predictions. These dissipative processes determine the Floquet band occupations of the emergent steady state, by balancing out the optical driving force. In order to benchmark and illustrate our framework for Floquet physics in a realistic solid, we consider the light-induced Hall conductivity in graphene recently reported by J.~W.~McIver, et al., Nature Physics (2020). We show that the Hall conductivity is estimated by the Berry flux of the occupied states of the light-induced Floquet bands, in addition to the kinetic contribution given by the average band velocity. Hence, Floquet theory provides an interpretation of this Hall conductivity as a geometric-dissipative effect. We demonstrate this mechanism within a master equation formalism, and obtain good quantitative agreement with the experimentally measured Hall conductivity, underscoring the validity of this approach which establishes a broadly applicable framework for the understanding of ultrafast non-equilibrium dynamics in solids.