The electronic band structures and optical absorption spectra for incommensurate twisted few-layers graphene

Abstract: A theoretical model is presented to compute the electronic band structures and optical absorption spectra for twisted incommensurate few-layers graphene (tLFG) systems of arbitrary architecture. This is accomplished using an integrated virtual crystal approximation and tight-binding (VCA-TB) method, where the VCA is achieved by a mathematical averaging formalism developed over the quasi-infinite ensemble of interlayer bond configurations. The results show that the low-energy electronic band structures of the incommensurate tLFG systems of N graphene layers are formed of N overlapping Dirac cones centered on the K-points of the Brillouin zones of the graphene layers. This yields effective gaps between the saddle points of the valence and conduction bands of these tFLG systems, that are tunable with the incommensurate twist angles. The optical absorption spectra are also calculated for these systems; in particular, they display clear spectral peaks which correspond to the accessible electronic transitions across the gaps between the valence and conduction bands. The optical absorption results highlight the potential of these incommensurate tFLG systems for applications in graphene based tandem cells.