Strain impacts on commensurate bilayer graphene superlattices: distorted trigonal warping, emergence of bandgap and direct-indirect bandgap transition

TL;DR

This study uses computational methods to explore how in-plane strain affects electronic properties of commensurate twisted bilayer graphene, revealing strain-dependent bandgap modifications and transitions.

Contribution

It provides new insights into strain effects on different classes of twisted bilayer graphene, highlighting the emergence of bandgaps and bandgap transitions based on stacking parity.

Findings

SE odd TBG remains gapless under strain

SE even TBG shows increased bandgap with tensile strain

Large mixed strains induce direct-indirect bandgap transition

Abstract

Due to low dimensionality, the controlled stacking of the graphene films and their electronic properties are susceptible to environmental changes including strain. The strain-induced modification of the electronic properties such as the emergence and modulation of bandgaps crucially depends on the stacking of the graphene films. However, to date, only the impact of strain on electronic properties of Bernal and AA-stacked bilayer graphene has been extensively investigated in theoretical studies. Exploiting density functional theory and tight-binding calculation, we investigate the impacts of in-plane strain on two different class of commensurate twisted bilayer graphene (TBG) which are even/odd under sublattice exchange (SE) parity. We find that the SE odd TBG remains gapless whereas the bandgap increases for the SE even TBG when applying equibiaxial tensile strain. Moreover, we observe that for extremely large mixed strains both investigated TBG superstructures demonstrate direct-indirect bandgap transition.