Coulomb drag in graphene near the Dirac point

TL;DR

This paper investigates Coulomb drag in double-layer graphene near the Dirac point, revealing a temperature-independent behavior in clean samples and complex disorder-dependent effects, including a peak at the Dirac point at low temperatures.

Contribution

It provides a detailed theoretical analysis of Coulomb drag in graphene near the Dirac point, highlighting the effects of electron-electron interactions and disorder using the quantum kinetic equation approach.

Findings

Drag becomes temperature-independent in the clean limit.

Disorder and temperature influence the dominance of different perturbative contributions.

A peak in Coulomb drag appears at the Dirac point at low temperatures.

Abstract

We study Coulomb drag in double-layer graphene near the Dirac point. A particular emphasis is put on the case of clean graphene, with transport properties dominated by the electron-electron interaction. Using the quantum kinetic equation framework, we show that the drag becomes $T$-independent in the clean limit, $T\tau \to \infty$, where $T$ is temperature and $1/\tau$ impurity scattering rate. For stronger disorder (or lower temperature), $T\tau \ll 1/\alpha^2$, where $\alpha$ is the interaction strength, the kinetic equation agrees with the leading-order ($\alpha^2$) perturbative result. At still lower temperatures, $T\tau \ll 1$ (diffusive regime) this contribution gets suppressed, while the next-order ($\alpha^3$) contribution becomes important; it yields a peak centered at the Dirac point with a magnitude that grows with lowering $T\tau$.