Observing light-induced Floquet band gaps in the longitudinal conductivity of graphene

TL;DR

This paper proposes using optical longitudinal conductivity measurements to detect light-induced Floquet band gaps in graphene, demonstrating how these gaps influence electron distributions and transport properties under strong driving fields.

Contribution

It introduces a realistic observable for detecting Floquet band gaps in graphene and interprets the electron distribution as occupations of Floquet-Bloch bands, advancing Floquet engineering.

Findings

Resonant features in conductivity reveal Floquet band gaps.

Population inversions occur at band gaps under strong driving.

Conductivity decreases at specific frequencies due to band inversions.

Abstract

We propose optical longitudinal conductivity as a realistic observable to detect light-induced Floquet band gaps in graphene. These gaps manifest as resonant features in the conductivity, when resolved with respect to the probing frequency and the driving field strength. We demonstrate these features via a dissipative master equation approach which gives access to a frequency- and momentum-resolved electron distribution. This distribution follows the light-induced Floquet-Bloch bands, resulting in a natural interpretation as occupations of these bands. Furthermore, we show that there are population inversions of the Floquet-Bloch bands at the band gaps for sufficiently strong driving field strengths. This strongly reduces the conductivity at the corresponding frequencies. Therefore our proposal puts forth not only an unambiguous demonstration of light-induced Floquet-Bloch bands, which advances the field of Floquet engineering in solids, but also points out the control of transport properties via light, that derives from the electron distribution on these bands.