Coulomb drag in graphene near the Dirac point

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, $Tτ\to \infty$, where $T$ is temperature and $1/τ$ impurity scattering rate. For stronger disorder (or lower temperature), $Tτ\ll 1/α^2$, where $α$ is the interaction strength, the kinetic equation agrees with the leading-order ($α^2$) perturbative result. At still lower temperatures, $Tτ\ll 1$ (diffusive regime) this contribution gets suppressed, while the next-order ($α^3$) contribution becomes important; it yields a peak centered at the Dirac point with a magnitude that grows with lowering $Tτ$.

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