Metallic Coulomb Blockade Thermometry down to 10 mK and below

TL;DR

This paper reports on advanced metallic Coulomb blockade thermometers capable of operating at temperatures as low as 7.5 mK, demonstrating improved cooling techniques and insights into electron-phonon interactions at ultra-low temperatures.

Contribution

It introduces enhanced nuclear refrigeration methods and detailed measurements of CBTs across different resistances, extending thermometry into the sub-10 mK regime.

Findings

High-R devices cool to lower temperatures due to better noise isolation.

Electron-phonon cooling follows a T^5 dependence in high-R CBTs.

Minimum temperature achieved is 7.5 mK.

Abstract

We present an improved nuclear refrigerator reaching 0.3 mK, aimed at microkelvin nanoelectronic experiments, and use it to investigate metallic Coulomb blockade thermometers (CBTs) with various resistances R. The high-R devices cool to slightly lower T, consistent with better isolation from the noise environment, and exhibit electron-phonon cooling ~ T^5 and a residual heat-leak of 40 aW. In contrast, the low-R CBTs display cooling with a clearly weaker T-dependence, deviating from the electronphonon mechanism. The CBTs agree excellently with the refrigerator temperature above 20 mK and reach a minimum-T of 7.5 +/- 0.2 mK.