Carrier Transport in Two-Dimensional Graphene Layers

Carrier transport in gated 2D graphene monolayers is considered in the presence of scattering by random charged impurity centers with density n_i. Excellent quantitative agreement is obtained (for carrier density n>10¹²  cm^-2) with existing experimental data. The conductivity scales linearly with n/n_i in the theory. We explain the experimentally observed asymmetry between electron and hole conductivities, and the high-density saturation of conductivity for the highest mobility samples. We argue that the experimentally observed saturation of conductivity at low density arises from the charged impurity induced inhomogeneity in the graphene carrier density which becomes severe for n≲n_i∼10¹²  cm^-2.