Coexistence of van Hove singularities and superlattice Dirac points in a slightly twisted graphene bilayer

We consider the electronic structure of a slightly twisted graphene bilayer and show the coexistence of van Hove singularities (VHSs) and superlattice Dirac points in a continuum approximation. The graphene-on-graphene moir\'e pattern gives rise to a periodic electronic potential, which leads to the emergence of the superlattice Dirac points due to the chiral nature of the charge carriers. Because of the distinguishing real and reciprocal structures, the sublattice exchange even and sublattice exchange odd structures of the twisted graphene bilayer result in two different structures of the superlattice Dirac points. We calculate the effect of a strain on the low-energy electronic structure of the twisted graphene bilayer and demonstrate that the strain affects the position of the VHSs dramatically.