Correlated Coulomb drag in capacitively coupled quantum-dot structures

TL;DR

This paper presents a theoretical study of Coulomb drag in capacitively coupled quantum dots, revealing a mesoscopic mechanism driven by nonlocal cotunneling and the influence of lead couplings, consistent with recent experiments.

Contribution

The authors develop a master-equation approach including cotunneling and energy-dependent lead couplings to explain Coulomb drag in CQDs, identifying conditions and mechanisms for nonzero drag.

Findings

Drag current direction depends on lead couplings, not drive current.

The theory matches recent experimental observations in graphene CQD heterostructures.

Nonlocal cotunneling is key to Coulomb drag in these systems.

Abstract

We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach which accounts for higher-order tunneling (cotunneling) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multi-electron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters. Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments on Coulomb drag in CQD systems.