Topological flat bands in strained graphene: substrate engineering and optical control

TL;DR

This paper investigates how substrate-induced strain and optical control can engineer topological flat bands in graphene, revealing key geometric features and enabling tunable electronic and topological properties.

Contribution

It identifies the critical role of $C_{2z}$ symmetry breaking and continuous strain profiles in creating flat bands and topological phases in graphene, guiding experimental strain engineering.

Findings

Strong $C_{2z}$ symmetry breaking induces energy gaps and flat bands.

Continuous strain profiles produce connected pseudo-magnetic fields.

Circularly polarized light controls and reveals topological properties.

Abstract

The discovery of correlated phases in twisted moir\'e superlattices accelerated the search for low-dimensional materials with exotic properties. A promising approach uses engineered substrates to strain the material. However, designing substrates for tailored properties is hindered by the incomplete understanding of the relationship between substrate's shapes and electronic properties of the deposited materials. By analyzing effective models of graphene under periodic deformations with generic crystalline profiles, we identify strong $C_{2z}$ symmetry breaking as the critical substrate geometric feature for emerging energy gaps and quasi-flat bands. We find continuous strain profiles producing connected pseudo-magnetic field landscapes are important for band topology. We show that the resultant electronic and topological properties from a substrate can be controlled with circularly polarized light, which also offers unique signatures for identifying the band topology imprinted by strain. Our results can guide experiments on strain engineering for exploring interesting transport and topological phenomena.