Normal metal - superconductor tunnel junction as a Brownian refrigerator

TL;DR

This paper explores how a normal metal-superconductor tunnel junction can act as a Brownian refrigerator, using thermal noise to remove heat from a cold normal metal, with analytical and numerical analysis of its cooling performance.

Contribution

It introduces a novel Brownian refrigeration mechanism using NIS junctions driven by thermal noise, expanding the understanding of heat rectification in superconducting devices.

Findings

Analytical results for idealized high impedance environment

Numerical calculations for general resistor resistance R

Assessment of experimental feasibility of the effect

Abstract

Thermal noise generated by a hot resistor (resistance $R$) can, under proper conditions, catalyze heat removal from a cold normal metal (N) in contact with a superconductor (S) via a tunnel barrier. Such a NIS junction acts as Maxwell's demon, rectifying the heat flow. Upon reversal of the temperature gradient between the resistor and the junction the heat fluxes are reversed: this presents a regime which is not accessible in an ordinary voltage-biased NIS structure. We obtain analytical results for the cooling performance in an idealized high impedance environment, and perform numerical calculations for general $R$. We conclude by assessing the experimental feasibility of the proposed effect.