Abstract
Coulomb drag is a favored experimental probe of Coulomb interactions between layers of 2D materials. In reality, these layers display spatial charge density fluctuations known as puddles due to various imperfections. A theoretical formalism for incorporating density inhomogeneity into calculations has however not been developed, making the understanding of experiments difficult. Here, we remedy this by formulating an effective medium theory of drag that applies in all 2D materials. We show that a number of striking features at zero magnetic field in graphene drag experiment which have not been explained by existing literature emerge naturally within this theory. Applying the theory to a phenomenological model of exciton condensation, we show that the expected divergence in drag resistivity is replaced by a peak that diminishes with increasing puddle strength. Given that puddles are ubiquitous in 2D materials, this work will be useful for a wide range of future studies.
Highlights
Coulomb drag is a favored experimental probe of Coulomb interactions between layers of 2D materials
We demonstrate using a phenomenological model that puddles cause the divergence in drag resistivity expected upon exciton condensation to be re-normalized to a peak that goes down as the reciprocal of the puddle strength
Since height corrugations are ubiquitous in 2D materials[37] and these in turn lead to puddles[25], we expect that the present formalism will be useful for explaining many future 2D Coulomb drag experiments
Summary
Coulomb drag is a favored experimental probe of Coulomb interactions between layers of 2D materials. A theoretical formalism for incorporating density inhomogeneity into calculations has not been developed, making the understanding of experiments difficult We remedy this by formulating an effective medium theory of drag that applies in all 2D materials. We demonstrate using a phenomenological model that puddles cause the divergence in drag resistivity expected upon exciton condensation to be re-normalized to a peak that goes down as the reciprocal of the puddle strength These two example applications show that puddles must be taken into account in order to understand existing drag experiments on graphene and suggest that they will play a role in the behavior of drag resistivity in an exciton condensate. Since height corrugations are ubiquitous in 2D materials[37] and these in turn lead to puddles[25], we expect that the present formalism will be useful for explaining many future 2D Coulomb drag experiments
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