Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

TL;DR

This paper explores nonlinear thermoelectric effects in superconductor-ferromagnet tunnel junctions, revealing large effects and their potential for improved refrigeration through combined experimental and theoretical analysis.

Contribution

It provides new insights into nonlinear thermoelectric phenomena in superconductor-ferromagnet structures, highlighting their dependence on bias and thermal excitation, and suggests applications in efficient cooling.

Findings

Large thermoelectric effects observed in hybrid structures

Spin-dependent signals linked to spin-heat coupling

Reciprocal relation to superconductor/normal-metal microrefrigerators

Abstract

Thermoelectric effects result from the coupling of charge and heat transport, and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron-hole symmetry, which is usually quite small in metal structures, and vanishes at low temperatures. We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the depencence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction. Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators