Minimal conductivity of graphene: role of the Coulomb interaction

The effect of the Coulomb interaction on the zero-temperature low-frequency conductivity in undoped graphene is studied. We will show that the Coulomb interaction introduces a universal and positive leading logarithmic correction to the gaussian value of the dc conductivity [1]. This finding suggests that the origin of the unusually large minimal conductivity observed in graphene may be intrinsic, and arises from the Coulomb correction effectively cut off by finite temeperature/disorder/size effects. A mechanism of such a cutoff based on the non-trivial interplay between the Coulomb interaction and the ripples, both unavoidably present in the graphene sheet, will be briefly discussed. References: [1] I. F. Herbut, V. Juricic, and O. Vafek, arXiv.0707.4171.