Floquet bound states around defects and adatoms in graphene

TL;DR

This study investigates Floquet bound states around various defects in laser-irradiated graphene, revealing their chiral nature, dependence on defect shape and edge termination, and potential implications for topological bulk transport.

Contribution

It provides a comprehensive analysis of Floquet bound states around defects in graphene, combining analytical and numerical methods, and explores their dependence on defect characteristics and potential topological effects.

Findings

Bound states are chiral and increase with defect size.

Spectrum depends on defect edge termination.

Bound states' energies depend on adatom energy.

Abstract

Recent studies have focused on laser-induced gaps in graphene which have been shown to have a topological origin, thereby hosting robust states at the sample edges. While the focus has remained mainly on these topological chiral edge states, the Floquet bound states around defects lack a detailed study. In this paper we present such a study covering large defects of different shape and also vacancy-like defects and adatoms at the dynamical gap at $\hbar\Omega/2$ ($\hbar\Omega$ being the photon energy). Our results, based on analytical calculations as well as numerics for full tight-binding models, show that the bound states are chiral and appear in a number which grows with the defect size. Furthermore, while the bound states exist regardless the type of the defect's edge termination (zigzag, armchair, mixed), the spectrum is strongly dependent on it. In the case of top adatoms, the bound states quasi-energies depend on the adatoms energy. The appearance of such bound states might open the door to the presence of topological effects on the bulk transport properties of dirty graphene.