The nonlinear energy spectrum dependence of the optical conductivity in graphene

In this article, we present a theoretical study of the optical spectrum induced by electron-electron interaction in graphene, which can be compared with the case in a conventional two-dimensional electron gas (2DEG). It is found that in sharp contrast to the conventional 2DEG, two intra-and inter-band transition channels for optical transition via absorption scattering can be observed. The optical conductivity depends on the electron density, the linearity of the energy spectrum, and the broadening width. The dependence of the optical spectrum on radiation frequency and broadening width is discussed. Analytical and numerical results showed that the inter-band transition contribution to optical conductivity has a turning point at two times the Fermi energy where the Fermi energy position can be tuned by the gate voltage. And the intra-band contribution depends on nonlinear energy dispersion and broadening width obviously. (C) 2013 AIP Publishing LLC.