Plasmon and dielectric background inhomogeneity enhancement of Coulomb drag in graphene double-layer structures

The drag of massless fermions in graphene double-layer structures is investigated in a wide rage of temperatures and inter-layer separations. We show that the inhomogeneity of the dielectric background in such graphene structures for experimentally relevant parameters results in a significant enhancement of the drag resistivity. At intermediate temperatures the dynamical screening via plasmon-mediated drag enhances the drag resistivity and results in an upturn in its behavior at large inter-layer separations. In a range of inter-layer separations, corresponding to the strong-to-weak crossover coupling of graphene layers, we find that the drag resistivity decreases approximately quadratically with the inter-layer spacing. This dependence weakens with a decrease of the inter-layer spacing while for larger separations we recover the cubic (quartic) dependence at intermediate (low) temperatures.