Nanoelectronic thermometers optimised for sub-10 millikelvin operation

TL;DR

This paper demonstrates the successful cooling of nanoelectronic Coulomb blockade thermometers to electron temperatures as low as 3.7 mK using an optimized design with cooling fins and electronic filters, surpassing previous limits.

Contribution

The study introduces an optimized nanoelectronic thermometer design enabling operation below 4 mK, achieving a lowest electron temperature of 3.7 mK.

Findings

Thermometers are well thermally coupled above 7 mK.

Cooling fins and filters improve low-temperature performance.

Electron temperature diverges from ambient below 7 mK.

Abstract

We report the cooling of electrons in nanoelectronic Coulomb blockade thermometers below 4 mK. Above 7 mK the devices are in good thermal contact with the environment, well isolated from electrical noise, and not susceptible to self-heating. This is attributed to an optimised design that incorporates cooling fins with a high electron-phonon coupling and on-chip electronic filters, combined with a low-noise electronic measurement setup. Below 7 mK the electron temperature is seen to diverge from the ambient temperature. By immersing a Coulomb Blockade Thermometer in the 3He/4He refrigerant of a dilution refrigerator, we measure a lowest electron temperature of 3.7 mK.