Topological Floquet Flat Bands in Irradiated Alternating Twist Multilayer Graphene

TL;DR

This paper explores how circularly polarized laser irradiation can induce topological Floquet flat bands with nonzero Chern numbers in alternating-twist multilayer graphene, offering a new route to realize fractional Chern insulators.

Contribution

It demonstrates the emergence of topological Floquet flat bands in alternating-twist multilayer graphene under laser irradiation, highlighting their potential for experimental observation and fractional Chern insulator realization.

Findings

Floquet flat bands with nonzero Chern numbers can be induced by laser in the system.

Topological flat bands are well-isolated in 3-5 layer configurations.

Potential experimental observation of dynamically generated topological flat bands.

Abstract

We study the appearance of topological Floquet flat bands in alternating-twist multilayer graphene, which has alternating relative twist angle $\pm\theta$ near the first magic angle. While the system hosts both flat bands and a steep Dirac cone in the static case, the circularly polarized laser beam can open a gap at the Moir\'{e} $K$ point and create Floquet flat bands carrying nonzero Chern numbers. Considering recent lattice-relaxation results, we find that the topological flat band is well-isolated for the effective interlayer tunneling in $n=3, 4, 5$ layers. Such dynamically produced topological flat bands are potentially observed in the experiment and thus provide a feasible way to realize the fractional Chern insulator.