Floquet Spectrum and Transport Through an Irradiated Graphene Ribbon

TL;DR

This paper investigates the Floquet spectrum and transport phenomena in irradiated graphene ribbons, revealing topological edge states, super-diffusive behavior at low frequencies, and ballistic transport in long ribbons.

Contribution

It provides a detailed analysis of Floquet topological properties and transport mechanisms in irradiated graphene, highlighting edge state dominance and unique conductivity behaviors.

Findings

Presence of topological edge states in irradiated graphene

Super-diffusive transport near zero energy at low frequencies

Ballistic transport regime in long graphene ribbons

Abstract

Graphene subject to a spatially uniform, circularly-polarized electric field supports a Floquet spectrum with properties akin to those of a topological insulator, including non-vanishing Chern numbers associated with bulk bands and current-carrying edge states. Transport properties of this system however are complicated by the non-equilibrium occupations of the Floquet states. We address this by considering transport in a two-terminal ribbon geometry for which the leads have well-defined chemical potentials, with an irradiated central scattering region. We demonstrate the presence of edge states, which for infinite mass boundary conditions may be associated with only one of the two valleys. At low frequencies, the bulk DC conductivity near zero energy is shown to be dominated by a series of states with very narrow anticrossings, leading to super-diffusive behavior. For very long ribbons, a ballistic regime emerges in which edge state transport dominates.