Phase-tunable thermoelectricity in a Josephson junction

G Marchegiani,A Braggio,F Giazotto

doi:10.1103/physrevresearch.2.043091

Abstract

Superconducting tunnel junctions constitute the units of superconducting quantum circuits and are massively used both for quantum sensing and quantum computation. In previous works, we predicted the existence of a nonlinear thermoelectric effect in a electron-hole symmetric system, namely, a thermally biased tunnel junction between two different superconductors, where the Josephson effect is suppressed. In this paper we investigate the impact of the phase-coherent contributions on the thermoelectric effect, by tuning the size of the Josephson coupling changing the flux of a direct-current Superconducting Quantum Interference Device (dc-SQUID). For a suppressed Josephson coupling, the system generates a finite average thermoelectric signal, combined to an oscillation due to the standard ac Josephson phenomenology. At large Josephson couplings, the thermoelectricity induces an oscillatory behaviour with zero average value of the current/voltage with an amplitude and a frequency associated to the Josephson coupling strength, and ultimately tuned by the dc-SQUID magnetic flux. In conclusion, we demonstrate to be able to control the dynamics of the spontaneous breaking of the electron-hole symmetry. Furthermore, we compute how the flux applied to the dc-SQUID and the lumped elements of the circuit determine the frequency of the thermoelectric signal across the structure, and we envision a frequency modulation application.

Highlights

The investigation of thermal transport in micro- and nanoscale systems has attracted growing interest in recent decades [1,2,3,4,5,6,7,8] and is expected to have an impact on the performance of modern quantum technologies [9,10]
The charge current in a tunnel junction between two superconductors depends both on the phase bias (φ) and the voltage (V ) applied to the junction, as first predicted by Josephson
We have discussed the dynamics of thermally biased Josephson junctions, in the presence of the nonlinear thermoelectric effect recently predicted in tunnel junctions between two different BCS superconductors

Summary

Introduction

The investigation of thermal transport in micro- and nanoscale systems has attracted growing interest in recent decades [1,2,3,4,5,6,7,8] and is expected to have an impact on the performance of modern quantum technologies [9,10]. Hybrid superconducting junctions [11,12] are ideal platforms for quantum devices [13,14,15,16], due to the well-established fabrication techniques and a precise modeling of the coherent electronic transport. They offer a tight control over thermal currents, with applications to electronic solid-state cooling [2,3], phase-coherent modulation of thermal currents [17,18], and quantum sensing [19]. The frequency and the amplitude of the thermoelectric-induced oscillations are numerically computed, and approximate expressions are obtained in some limiting cases

Objectives

Results

Conclusion