Investigation of the effects of the graphene-substrate hybridization on the optical conductivity of graphene

Graphene is an emerging two-dimensional material with a lot of promising applications as devices, in which it must be combined with other materials, most notably put on top of a substrate. Recent research has shown that certain substrates can change the physical properties of graphene dramatically. Here, we propose a simple model describing a system of single layer graphene on top of a layered insulating substrate based on the tight-binding approximation, where we introduce a hybridization term of the graphene 2p_z orbital and topmost substrate layer orbitals. We then calculate the density of states DOS (ν) and the real part of the optical conductivity tensor σ₁^ab(ω) of the graphene layer for various values of the substrate band gap. The results show that the graphene-substrate hybridization tends to create states around the Fermi energy, thus enhancing the DC conductivity of the graphene layer. Furthermore, the peak in the σ₁^aa(ω) of graphene tends to get renormalized and experience a redshift, most prominently when the substrate band gap matches twice the graphene nearest-neighbor hopping parameter t_g. Meanwhile, an insulating substrate with a very high band gap (around 4t_g) weakens the effects of the hybridization.