Non-invasive thermometer based on proximity superconductor for ultra-sensitive calorimetry

TL;DR

This paper introduces a non-invasive radio-frequency thermometry technique using a superconductor-normal metal tunnel junction, enabling ultra-sensitive temperature measurements down to 25 mK without dissipation issues.

Contribution

It presents a novel zero bias anomaly-based thermometry method that overcomes dissipation and sensitivity loss at low temperatures, extending measurement capabilities.

Findings

Zero bias anomaly thermometry works down to 25 mK.

It measures local electron temperature accurately.

It avoids dissipation issues of finite-bias thermometers.

Abstract

We present radio-frequency thermometry based on a tunnel junction between a superconductor and proximitized normal metal. It allows operation in a wide range of biasing conditions. We demonstrate that the standard finite-bias quasiparticle tunneling thermometer suffers from large dissipation and loss of sensitivity at low temperatures, whereas thermometry based on zero bias anomaly avoids both these problems. For these reasons the latter method is suitable down to lower temperatures, here to about 25 mK. Both thermometers are shown to measure the same local temperature of the electrons in the normal metal in the range of their applicability.