Floquet-Engineered Topological Flat Bands in Irradiated Twisted Bilayer Graphene

TL;DR

This paper proposes an optical method to create and control topologically nontrivial flat bands in twisted bilayer graphene using circularly polarized light, enabling tunable strongly correlated phases.

Contribution

It introduces a tunable optical setup to engineer topological flat bands in twisted bilayer graphene, demonstrating control over flatness, gaps, and topology via laser parameters.

Findings

Flat bands can be engineered at small twist angles near magic angles.

Flatness and gaps are tunable by laser frequency and amplitude.

Flat bands carry nonzero Chern numbers under circularly polarized UV light.

Abstract

We propose a tunable optical setup to engineer topologically nontrivial flat bands in twisted bilayer graphene under circularly polarized light. Using both analytical and numerical calculations, we demonstrate that nearly flat bands can be engineered at small twist angles near the magic angles of the static system. The flatness and the gaps between these bands can be tuned optically by varying laser frequency and amplitude. We study the effects of interlayer hopping variations on Floquet flat bands and find that lattice relaxation favors their formation. Furthermore, we find that, once formed, the flat bands carry nonzero Chern numbers. We show that at currently known values of parameters, such topological flat bands can be realized using circularly polarized UV laser light. Thus, our work opens the way to creating optically tunable, strongly correlated topological phases of electrons in moir\'e superlattices.