Large Tunable Thermophase in Superconductor -- Quantum Dot -- Superconductor Josephson Junctions

TL;DR

This paper theoretically demonstrates a highly tunable thermoelectric effect in a superconductor-quantum dot-superconductor Josephson junction, showing a large thermo-phase controllable by gate voltage, which could enable new thermoelectric applications.

Contribution

It introduces a model for a SC-QD-SC junction with tunable thermoelectric properties and derives exact thermo-phase and thermal response, revealing significantly enhanced effects compared to traditional junctions.

Findings

Thermo-phase can reach up to π/2 with gate tuning.

Thermal response is orders of magnitude larger than in standard SC junctions.

Thermoelectric effects are controllable via quantum dot energy levels.

Abstract

In spite of extended efforts, detecting thermoelectric effects in superconductors have proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor -- Quantum Dot -- Superconductor (SC-QD-SC) Josephson Junction with highly tunable thermoelectric properties and a thermal response that is far larger than previous suggestions. The QD energy level between the SCs breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of $\pi/2$ after which thermovoltage is expected to develop. Using time-independent Keldysh countour Green's functions we derive the exact thermo-phase and thermal response on the junction. These are shown to be orders of magnitude larger than usual SC tunnel junctions with a sharp dependence on gate voltage.