The effect of next nearest neighbor coupling on the optical spectra in bilayer graphene

We investigate the dependence of the optical conductivity of bilayer graphene (BLG) on the intra and interlayer interactions using the most complete model to date. We show that the next nearest neighbor intralayer coupling introduces new features in the low energy spectrum significantly changing the 'universal' conductance. Further, its interplay with interlayer couplings leads to an anisotropy in the conductance in the ultraviolet range. We propose that experimental measurement of the optical conductivity of intrinsic and doped BLG will provide a good benchmark for the relative importance of intra and interlayer couplings at different doping levels.