Enhanced Optical Conductivity Induced by Surface States in ABC-stacked Few-Layer Graphene

The surface states of ABC-stacked few-layer graphene (FLG) are studied based on density-functional theory. These states form flat bands near the Fermi level, with the k-space range increasing with the layer number. Based on a tight-binding model, the characteristics of these surface states and their evolution with respect to the number of layers are examined. The infrared optical conductivity is then calculated within the single-particle excitation picture. We show that the surface states introduce unique peaks at around 0.3 eV in the optical conductivity spectra of ABC-stacked FLG when the polarization is parallel to the sheets, in good agreement with recent experimental measurement. Furthermore, as the layer number increases, the absorption amplitude is greatly enhanced and the peak position red-shifts, which provides a feasible way to identify the number of layers for ABC-stacked FLG using optical conductivity measurements.