Out-of-equilibrium nonlinear model of thermoelectricity in superconducting tunnel junctions

TL;DR

This paper develops a comprehensive out-of-equilibrium nonlinear model for thermoelectric effects in superconducting tunnel junctions, revealing significant deviations from traditional linear models at high power levels and introducing new criteria for nonlinear thermoelectricity.

Contribution

The paper introduces a novel out-of-equilibrium nonlinear numerical model that extends beyond the linear approximation, providing more accurate descriptions of superconducting tunnel junctions under realistic conditions.

Findings

Linear models fail at high power regimes.

Junctions saturate and invert behavior at high power.

New criteria for identifying nonlinear thermoelectricity.

Abstract

Thermoelectricity in superconducting tunnel junctions has always been studied under the hypothesis of equilibrium between the cold side and the thermal bath, usually in the linear regime. We define a more complete out-of-equilibrium nonlinear numerical model that reduces to the equilibrium linear model in the low-power limit. We find that the linear model does not correctly describe the behavior of superconducting tunnel junctions for parameters that are reasonable in practical experimental setups. Subsequently, we present the qualitative and quantitative differences between the models, discovering that for high power, the junction saturates and then inverts its behavior. Finally, we also clarify the difference between linear and nonlinear thermoelectricity and devise a new criterion to find nonlinear thermoelectricity in the parameter space.