  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.
