Valley-selective Floquet Chern Flat Bands in Twisted Multilayer Graphene

TL;DR

This paper demonstrates how circularly polarized light can be used to engineer valley-polarized Floquet Chern flat bands in twisted multilayer graphene, enabling optical control of valley-related properties and topological phases.

Contribution

It introduces a method to selectively manipulate valley degeneracy and generate tunable Chern flat bands in TMG using Floquet engineering with CPL, revealing a hierarchy rule and dependence on stacking chirality.

Findings

CPL can induce valley-selective splitting in TMG.

A hierarchy rule for Chern numbers in Floquet flat bands is established.

Effects depend on stacking chirality, testable in twisted double bilayer graphene.

Abstract

We show that Floquet engineering with circularly polarized light (CPL) can selectively split the valley degeneracy of a twisted multilayer graphene (TMG), and thus generate a controlled valley-polarized Floquet Chern flat band with tunable large Chern number. It offers a feasible optical way to manipulate the valley degree of freedom in moir\'{e} flat bands, and hence opens new opportunities to study the valleytronics of mori\'{e} flat band systems. We thus expect that many of the valley-related properties of TMG, e.g. orbital ferromagnetism, can be switched by CPL with proper doping. We reveal a Chern number hierarchy rule for the Floquet flat bands in a generic (M+N)-layer TMG. We also illustrate that the CPL effects on TMG strongly rely on the stacking chirality, which is an unique feature of TMG. All these phenomena could be tested in the twisted double bilayer graphene systems, which is the simplest example of TMG and has already been realized in experiment.