Conductivity of suspended and non-suspended graphene at finite gate voltage

Abstract

We compute the dc and the optical conductivity of graphene for finite values of the chemical potential by taking into account the effect of disorder, due to midgap states (unitary scatterers) and charged impurities, and the effect of both optical and acoustic phonons. The disorder due to midgap states is treated in the coherent-potential approximation (a self-consistent approach based on the Dyson equation) whereas that due to charged impurities is also treated via the Dyson equation with the self-energy computed using second-order perturbation theory. The effect of the phonons is also included via the Dyson equation with the self-energy computed using first-order perturbation theory. The self-energy due to phonons is computed both using the bare electronic Green's function and the full electronic Green's function although we show that the effect of disorder on the phonon propagator is negligible. Our results are in qualitative agreement with recent experiments. Quantitative agreement could be obtained if one assumes water molecules under the graphene substrate. We also comment on the electron-hole asymmetry observed in the dc conductivity of suspended graphene.