Micrometre-scale refrigerators

TL;DR

This paper reviews the principles, experimental conditions, and recent advancements in micrometre-scale superconducting coolers that operate at sub-kelvin temperatures, highlighting their potential for on-chip cooling applications.

Contribution

It provides a comprehensive overview of the experimental progress and practical challenges in developing micrometre-scale superconducting coolers over the past five years.

Findings

Identification of key experimental conditions for cooler performance

Analysis of main practical limitations affecting efficiency

Summary of recent experimental advancements in the field

Abstract

A superconductor with a gap in the density of states or a quantum dot with discrete energy levels is a central building block in realizing an electronic on-chip cooler. They can work as energy filters, allowing only hot quasiparticles to tunnel out from the electrode to be cooled. This principle has been employed experimentally since the early 1990s in investigations and demonstrations of micrometre-scale coolers at sub-kelvin temperatures. In this paper, we review the basic experimental conditions in realizing the coolers and the main practical issues that are known to limit their performance. We give an update of experiments performed on cryogenic micrometre-scale coolers in the past five years.