Optically induced flat bands in twisted bilayer graphene

TL;DR

This paper demonstrates that coherent optical illumination can induce flat Floquet-Bloch bands in twisted bilayer graphene, broadening the twist angle range for flat band formation and enabling new strongly-correlated electronic states.

Contribution

It introduces a mechanism using optical illumination to create flat bands in twisted bilayer graphene, increasing the twist angle tolerance significantly.

Findings

Optical illumination induces flat Floquet-Bloch bands in twisted bilayer graphene.

The effect works with weak visible-infrared light and persists over a wide twist angle range.

Induced bands can have non-zero Chern numbers, enabling topological states.

Abstract

Twisted Bilayer Graphene at the magic twist angle features flat energy bands, which lead to superconductivity and strong correlation physics. These unique properties are typically limited to a narrow range of twist angles around the magic angle with a small allowed tolerance. Here we report on a mechanism that enables flattening of the band-structure using coherent optical illumination, leading to emergence of flat isolated Floquet-Bloch bands. We show that the effect can be realized with relatively weak optical beams at the visible-infrared range (below the material bandwidth) and persist for a wide range of small twist angles, increasing the allowed twist tolerance by an order of magnitude. We discuss the conditions under which these bands exhibit a non-zero Chern number. These optically induced flat bands could potentially host strongly-correlated, non-equilibrium electronic states of matter.