ABSTRACT
In this work, the optical responses of graphene superlattices, i.e. graphene subjected to a periodic scalar potential, are theoretically reported. The optical properties were studied by investigating the optical conductivity, which was calculated using the Kubo formalism. It was found that the optical conductivity becomes dependent on the photon polarization and is suppressed in the photon energy range of (0, Ub), where Ub is the potential barrier height. In the higher photon energy range, i.e. Ω > Ub, the optical conductivity is, however, almost identical to that of pristine graphene. Such behaviors of the optical conductivity are explained microscopically through the analysis of the elements of optical matrices and effectively through a simple model, which is based on the Pauli blocking mechanism.
ABSTRACT
In this work, the effect of coupling between metallic electrodes and graphene is discussed. We demonstrate that the transport properties of graphene at the charge neutrality point are very sensitive to this coupling. By introducing a model based on two real parameters, namely the real and the imaginary parts of the self-energy which describes the metal-graphene coupling, the obtained results of charge conductivity versus the Fermi energy reproduce well the essential features of experimental data such as the asymmetry between electrons and holes. Additionally, the possible role of scattering processes in the enhancement of the density of states, and thus of the minimum of conductivity, at the charge neutrality point is also discussed. This work is believed to be helpful for further studies of graphene-based devices wherein metallic electrodes may have a major impact on electrical characteristics.
