Effects of pressure and heterostrain on electronic bands of twisted bilayer graphene

We study the effects of pressure and uniaxial heterostrain on the energy bands and density of states in twisted bilayer graphene based on the effective continuum model. We find that extremely flat bands (one tenth of the bandwidth at magic angle 1.05 degrees) can be achieved under pressure for a wide range of twist angles due to the enhancement of interlayer coupling strength. Under strain, pressure dramatically reduces the separation and widths of the flatband van Hove singularities at angles beyond the magic angle. Strain direction provides an addition parameter for tuning the flat bands to realize narrow bandwidth. Moreover, high-order van Hove singularities favoring strong electron correlations can be managed by applying pressure and strain. These effects may promote correlated electron phenomena at a broad range of twist angles.& COPY; 2023 Elsevier B.V. All rights reserved.