Phase-tunable thermoelectricity in a Josephson junction

TL;DR

This paper explores how phase coherence influences thermoelectric effects in superconducting Josephson junctions, demonstrating tunable thermoelectric signals controlled by magnetic flux and Josephson coupling, with potential for frequency modulation applications.

Contribution

It reveals the impact of phase-coherent contributions on thermoelectricity in Josephson junctions and shows how to control thermoelectric signals via magnetic flux and Josephson coupling.

Findings

Thermoelectric signal can be controlled by Josephson coupling strength.

Flux tuning enables frequency modulation of thermoelectric signals.

Phase coherence affects the symmetry breaking and oscillatory behavior.

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.