Bipolar Thermoelectricity in Bilayer-Graphene/Superconductor Tunnel Junctions

Abstract

We investigate the thermoelectric properties of a hybrid nanodevice composed by a 2D carbonbased material and a superconductor. This system presents nonlinear bipolar thermoelectricity as induced by the spontaneous breaking of the Particle-Hole (PH) symmetry in a tunnel junction between a BiLayer Graphene (BLG) and a Bardeen-Cooper-Schrieffer (BCS) superconductor. In this scheme, the nonlinear thermoelectric effect, predicted and observed in SIS' junctions is not affected by the competitive effect of the Josephson coupling. From a fundamental perspective, the most intriguing feature of this effect is its bipolarity, that poses new issues on the nature of thermoelectricity in solid state systems. The capability to open and control the BLG gap guarantees improved thermoelectric performances, that reach up to 1 mV/K regarding the Seebeck coefficient and a power density of 1 nW/µm 2 for temperature gradients of tens of Kelvins. Furthermore, the externally controlled gating can also dope the BLG, which is otherwise intrinsically PH symmetric, giving us the opportunity to investigate the bipolar thermoelectricity even in presence of a controlled suppression of the PH symmetry. The predicted robustness of this system could foster further experimental investigations and applications in the near future, thanks to the available techniques of nano-fabrication.

Phase-control of bipolar thermoelectricity in Josephson tunnel junctions

“…Yet, the above described bipolar thermoelectric effect is expected to occur as well in several thermally-biased physical systems, which are characterized by an intrinsic PH symmetry, and where the hot and cold electrodes possess a gapped and monotonicallydecreasing density of states, respectively [34]. For this reason, our study is pivotal for groundbreaking investigations of nonlinear thermoelectric effects in a number of different solid-state systems ranging from semiconductors and low-dimensional electronic materials [65] to hightemperature superconductors and topological insulators.…”

Hybrid normal-superconducting Aharonov-Bohm quantum thermal device

“…Engineering versatile and efficient quantum thermal devices to manage heat at the nanoscale is highly challenging and relevant for future quantum technologies [1][2][3]. Controlling heat implies, in particular, being able to exploit a temperature gradient as a resource for operating a device as heat engine [4][5][6][7][8][9], and to allow for preferential heat flow in one direction under thermal biasing, a feature known as thermal rectification [1,10,11]. Both abilities have been investigated independently from each other, motivating numerous proposals and experiments that exploit various platforms with the objective of managing heat at the nanoscale in an efficient way.…”

“…As recent examples, we emphasize achievements with superconducting circuit QED setups [10,12,13], with superconducting-semiconducting devices [14][15][16] and with graphene-based samples [17] for heat rectification. The first experimental heat engines at the nanoscale have exploited among others features trapped ions [18,19] and cold atoms [20], NV-centers samples [21], semiconducting quantum dots [5] and, very recently, superconducting tunnel junctions [7].…”