Theory of Coulomb drag for massless Dirac fermions

TL;DR

This paper develops a minimal theoretical model for Coulomb drag between two graphene sheets with massless Dirac fermions, analyzing low-temperature behavior and effects of dielectric environments, and proposes experimental tests.

Contribution

It provides a pedagogical and analytical framework for Coulomb drag in Dirac fermion systems, including effects of spacer thickness and dielectric properties, extending previous results.

Findings

Drag transresistivity is insensitive to intralayer scattering mechanisms at low temperatures.

Analytical formulas for drag in different spacer thicknesses and dielectric constants.

Numerical results for frequency-dependent dielectric media.

Abstract

Coulomb drag between two unhybridized graphene sheets separated by a dielectric spacer has recently attracted considerable theoretical interest. We first review, for the sake of completeness, the main analytical results which have been obtained by other authors. We then illustrate pedagogically the minimal theory of Coulomb drag between two spatially-separated two-dimensional systems of massless Dirac fermions which are both away from the charge-neutrality point. This relies on second-order perturbation theory in the screened interlayer interaction and on Boltzmann transport theory. In this theoretical framework and in the low-temperature limit, we demonstrate that, to leading (i.e. quadratic) order in temperature, the drag transresistivity is completely insensitive to the precise intralayer momentum-relaxation mechanism (i.e. to the functional dependence of the scattering time on energy). We also provide analytical results for the low-temperature drag transresistivity for both cases of "thick" and "thin" spacers and for arbitrary values of the dielectric constants of the media surrounding the two Dirac-fermion layers. Finally, we present numerical results for the low-temperature drag transresistivity in the case in which one of the media surrounding the Dirac-fermion layers has a frequency-dependent dielectric constant. We conclude by suggesting an experiment that can potentially allow for the observation of departures from the canonical Fermi-liquid quadratic-in-temperature behavior of the transresistivity.