Strain-induced modulation of Dirac cones and van Hove singularities in a twisted graphene bilayer

By means of atomistic calculations, we investigate the effects of uniaxial strain on the electronic bandstructure of a twisted graphene bilayer (T-GBL). We find that the bandstructure is dramatically deformed and the degeneracy of the bands around the Dirac points is broken by strain. As a consequence, the number of valleys in the bandstructure can double and the van Hove singularity (VHS) points are separated in energy. The dependence of these effects on the magnitude of strain, its applied direction and the twist angle is carefully examined and clarified. As an important result, we demonstrate that the position of VHSs can be modulated by strain, suggesting the possibility of observing this peculiar feature of the bandstructure at low energy in a large range of twist angles (i.e., larger than 10 degrees). These phenomena could not be detected within the continuum approximation used in previous works. While they are in good agreement with available experimental data, our results provide a detailed understanding of the strain effects on the electronic properties of T-GBLs and may motivate further investigations of electronic transport in this type of graphene lattice.