Many-electron Effects on the Electronic Structure and Optical Spectrum of Few-layer Graphene*

We present a first-principles calculation of the optical properties of single- and few-layer graphene with many-electron effects included, employing the GW-Bethe Salpeter equation (GW- BSE) approach. We have found enhanced excitonic effects that result in significant changes in the optical absorption of few- layer graphene as compared to the independent-particle picture. Our calculated absorption spectrum is in good agreement with recent experiments. This study is of importance for understanding excitonic effects in two-dimensional semimetal systems and expected to be useful for possible optoelectronics applications of graphene.