Inherent thermometry in a hybrid superconducting tunnel junction

TL;DR

This paper explores a method for measuring electron temperature directly within a superconductor-normal metal-superconductor tunnel junction without additional thermometers, using the junction's inherent properties and current-voltage characteristics.

Contribution

It introduces a novel approach to inherent thermometry in S-N-S junctions, eliminating the need for external thermometers and analyzing the limits of this method.

Findings

Electron temperature can be inferred from I-V characteristics without additional thermometers.

The method's validity depends on junction symmetry, Andreev reflection, and sub-gap states.

Experimental results align with theoretical predictions under certain conditions.

Abstract

We discuss inherent thermometry in a Superconductor - Normal metal - Superconductor tunnel junction. In this configuration, the energy selectivity of single-particle tunneling can provide a significant electron cooling, depending on the bias voltage. The usual approach for measuring the electron temperature consists in using an additional pair of superconducting tunnel junctions as probes. In this paper, we discuss our experiment performed on a different design with no such thermometer. The quasi-equilibrium in the central metallic island is discussed in terms of a kinetic equation including injection and relaxation terms. We determine the electron temperature by comparing the micro-cooler experimental current-voltage characteristic with isothermal theoretical predictions. The limits of validity of this approach, due to the junctions asymmetry, the Andreev reflection or the presence of sub-gap states are discussed.