Topologically trivial and nontrivial edge bands in graphene induced by irradiation

TL;DR

This paper models how different polarizations of light induce topologically trivial or nontrivial edge bands in graphene, revealing the conditions under which these edge states appear and their topological nature.

Contribution

It introduces a minimal Floquet model for light-induced band structures in graphene, distinguishing between trivial and topological edge states based on light polarization.

Findings

Linearly polarized light creates pseudo gaps with flat or curved edge bands depending on ribbon orientation.

Circularly polarized light induces helical edge bands within real gaps.

The topological nature of edge bands is characterized by the Chern number and winding number.

Abstract

We proposed a minimal model to describe the Floquet band structure of two-dimensional materials with light-induced resonant inter-band transition. We applied it to graphene to study the band features caused by the light irradiation. Linearly polarized light induces pseudo gaps (gaps are functions of wavevector), and circularly polarized light causes real gaps on the quasi-energy spectrum. If the polarization of light is linear and along the longitudinal direction of zigzag ribbons, flat edge bands appear in the pseudo gaps, and if is in the lateral direction of armchair ribbons, curved edge bands can be found. For the circularly polarized cases, edge bands arise and intersect in the gaps of both types of ribbons. The edge bands induced by the circularly polarized light are helical and those by linearly polarized light are topologically trivial ones. The Chern number of the Floquet band, which reflects the number of pairs of helical edge bands in graphene ribbons, can be reduced into the winding number at resonance.