Engineering drag currents in Coulomb coupled quantum dots

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.

Fluctuation-driven Coulomb drag in interacting quantum dot systems

“…Conclusions.-We have studied Coulomb drag across interaction regimes in Coulomb-coupled QD systems in the framework of the Keldysh NEGF technique. In agreement with previous works [12,[19][20][21], we find that drag is an inherently nonlinear effect and that energy-dependent lead couplings are instrumental for the generation of a drag current. As we demonstrate, the drag is driven by the nonequilibrium charge fluctuations of the drive QD, and we discuss how the characteristics of the quantum noise allows to differentiate the drag mechanism discussed here from drag induced by a circuit environment [17] experimentally.…”

“…where ∆Γ j = Γ Lj − Γ Rj . This can be viewed as drag due to nonlocal cotunneling processes where the pseudospin of the DQD is flipped in one coherent processes via virtual intermediate empty and filled states [20,21].…”

“…This development has led to a revival of the phenomenon of Coulomb drag [10] in nanoscale systems with several reports of drag currents-i.e., a current induced in an unbiased drag system by its Coulomb interaction with a biased current-carrying drive system-in Coulomb-coupled double quantum dot (DQD) systems in 2DEGs [11,12] as well as in graphene and carbon nanotubes [13,14]. Theoretically, drag in quantum conductors [15][16][17][18] and QD systems [12,[19][20][21] has been studied thoroughly, with indications of an intimate link [17,22] between drag and the quantum noise of nonequilibrium fluctuations [23,24].…”

Generalized Master Equation Approach to Time-Dependent Many-Body Transport

“…After using the GME formalism to describe transient transport via excited states in a single interacting nanowire we now extend its applications to capacitively coupled quantum systems. Besides Coulomb blockade, the electron-electron interaction cause momentum-exchange which leads to the well known Coulomb drag effect in double-layer structures [ 62 ] and double quantum dots [ 63 , 64 , 65 ] or wires [ 66 ]. Also, theoretical calculations on thermal drag between Coulomb-coupled systems were recently presented [ 67 , 68 ].…”

Effective Equilibrium in Out-of-Equilibrium Interacting Coupled Nanoconductors

“…The detection of this drag current has been demonstrated experimentally [ 17 ] showing that high-order tunneling events such as cotunneling have a significant contribution. Besides, a drag current control has been proposed by attaching to the dots different materials with nontrivial energy-dispersion relations [ 18 ]. This system has additionally been proposed for the implementation of a Maxwell demon [ 19 ], in which one of the dots (the demon) acquires information from the other one, allowing a current to flow opposite to the applied bias voltage in the other dot.…”