Brownian refrigeration by hybrid tunnel junctions

TL;DR

This paper investigates how voltage fluctuations in hybrid tunnel junctions can induce cooling of a normal metal electrode, analyzing effects of charging and shot noise, and discussing experimental feasibility.

Contribution

It extends previous analysis of Brownian refrigeration in hybrid junctions, including effects of charging and nonequilibrium shot noise, providing explicit analytic results.

Findings

Voltage fluctuations can extract heat from a cold electrode.

Charging effects influence cooling in single-electron transistors.

Shot noise can also induce cooling effects.

Abstract

Voltage fluctuations generated in a hot resistor can cause extraction of heat from a colder normal metal electrode of a hybrid tunnel junction between a normal metal and a superconductor. We extend the analysis presented in [Phys. Rev. Lett. 98, 210604 (2007)] of this heat rectifying system, bearing resemblance to a Maxwell's demon. Explicit analytic calculations show that the entropy of the total system is always increasing. We then consider a single electron transistor configuration with two hybrid junctions in series, and show how the cooling is influenced by charging effects. We analyze also the cooling effect from nonequilibrium fluctuations instead of thermal noise, focusing on the shot noise generated in another tunnel junction. We conclude by discussing limitations for an experimental observation of the effect.