Measurement Back-Action in Stacked Graphene Quantum Dots

Abstract

We present an electronic transport experiment in graphene where both classical and quantum mechanical charge detector back-action on a quantum dot are investigated. The device consists of two stacked graphene quantum dots separated by a thin layer of boron nitride. This device is fabricated by van der Waals stacking and is equipped with separate source and drain contacts to both dots. By applying a finite bias to one quantum dot, a current is induced in the other unbiased dot. We present an explanation of the observed measurement-induced current based on strong capacitive coupling and energy dependent tunneling barriers, breaking the spatial symmetry in the unbiased system. This is a special feature of graphene-based quantum devices. The experimental observation of transport in classically forbidden regimes is understood by considering higher order quantum mechanical back-action mechanisms.

Cotunneling Drag Effect in Coulomb-Coupled Quantum Dots

“…This rectification of nonequilibrium fluctuations is similar to a ratchet effect, as observed in charge- [15][16][17][18] and spin-based nanoelectronic devices [19], as well as in rather different contexts such as suspended colloidal particles in asymmetric periodic potentials [20]. Coulomb-coupled dots have also been proposed as a means for testing fluctuation relations out of equilibrium [1].An open question is how higher-order tunneling events in the quantum coherent limit contribute to Coulomb drag processes [21]. In this Letter, we present experimental measurements and theoretical arguments showing that simultaneous tunneling of electrons (cotunneling) is crucial to describe drag effects qualitatively in Coulomb-coupled double quantum dots (CC-DQDs).…”

“…In this Letter, we present experimental measurements and theoretical arguments showing that simultaneous tunneling of electrons (cotunneling) is crucial to describe drag effects qualitatively in Coulomb-coupled double quantum dots (CC-DQDs). Previous theoretical work has obtained drag effects with sequential tunneling models [1] (for an exception, see Ref.[22]), and these models have been invoked in measurements of stacked graphene quantum dots [21]. We demonstrate here that for a DQD, cotunneling contributes to the drag current at the same order as sequential tunneling in a perturbation expansion.…”

“…[22]), and these models have been invoked in measurements of stacked graphene quantum dots [21]. We demonstrate here that for a DQD, cotunneling contributes to the drag current at the same order as sequential tunneling in a perturbation expansion.…”

Engineering drag currents in Coulomb coupled quantum dots

“…However and in contrast to the theory of [37], the experiment shows at very low temperatures the importance of including cotunneling processes, as demonstrated with a theoretical model that shows excellent agreement with the experimental data [38]. The role of cotunneling processes is also emphasized in [39] where a similar system is considered but with graphene reservoirs instead of normal electron reservoirs [40]. In both cases, a four-charge state model within a master equation description serves as a theoretical basis to describe the Coulomb drag effect.…”

Thermoelectrics in Coulomb-coupled quantum dots: Cotunneling and energy-dependent lead couplings

“…However, energy-dependent couplings to the leads occur naturally in many QD systems [5,6,8,24] and add an important degree of tunability to the system. This is as crucial for the thermoelectric properties [10,11,25] as it is for Coulomb drag [5,6,[26][27][28].…”