Abstract
The Coulomb drag phenomenon in a Coulomb-coupled double quantum dot system is revisited with a simple model that highlights the importance of simultaneous tunneling of electrons. Previously, cotunneling effects on the drag current in mesoscopic setups have been reported both theoretically and experimentally. However, in both cases the sequential tunneling contribution to the drag current was always present unless the drag level position were too far away from resonance. Here, we consider the case of very large Coulomb interaction between the dots, whereby the drag current needs to be assisted by cotunneling events. As a consequence, a quantum coherent drag effect takes place. Further, we demonstrate that by properly engineering the tunneling probabilities using band tailoring it is possible to control the sign of the drag and drive currents, allowing them to flow in parallel or antiparallel directions. We also show that the drag current can be manipulated by varying the drag gate potential and is thus governed by electron- or hole-like transport.
Highlights
In a system made of two nearby isolated conductors where particles are prevented from tunneling into each other, a bias drop through one conductor can drag a current through the other conductor due to Coulomb interaction between them [1, 2]
We show that the drag transport in this configuration must be assisted by cotunneling mechanisms unlike the four-state model employed in previous works [37,38,39], in which sequential contributions to the drag current are always present
In the following we present our results for the drive and drag currents and discuss the tunability of the drag current depending on the system parameters
Summary
In a system made of two nearby (electrically) isolated conductors where particles are prevented from tunneling into each other, a bias drop through one conductor can drag a current through the other conductor due to Coulomb interaction between them [1, 2]. Coulomb drag between electrostatically coupled arrays of metalic tunnel junctions [28, 29], between quantum wire and quantum dot [30], between quantum dots [31], or between quantum point contacts [32] has been demonstrated. In such systems translational symmetry is broken. Energy exchange between the drive and drag subsystems leads to rectification of nonequilibrium fluctuations [33] in close analogy to the ratchet effect [34, 35] with possible energy harvesting applications [36]
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