Irradiated graphene as a tunable Floquet topological insulator

TL;DR

This paper demonstrates how irradiated graphene can be tuned into a Floquet topological insulator with controllable edge states using circularly polarized light, combining analytical, numerical, and topological analyses.

Contribution

It provides a comprehensive analysis of topologically protected edge states in irradiated graphene, revealing external control over their propagation and energy window.

Findings

Edge states appear inside dynamical gaps at specific photon energies.

Propagation direction of edge states is controlled by light polarization.

Analytical and numerical methods fully characterize these states.

Abstract

In the presence of a circularly polarized mid-infrared radiation graphene develops dynamical band gaps in its quasi-energy band structure and becomes a Floquet insulator. Here we analyze how topologically protected edge states arise inside these gaps in the presence of an edge. Our results show that the gap appearing at $\hbar\Omega/2$, where $\hbar \Omega$ is the photon energy, is bridged by two chiral edge states whose propagation direction is set by the direction of the polarization of the radiation field. Therefore, both the propagation direction and the energy window where the states appear can be controlled externally. We present both analytical and numerical calculations that fully characterize these states. This is complemented by simple topological arguments that account for them and by numerical calculations for the case of semi-infinite sample, thereby eliminating finite size effects.