Finite-bias Coulomb blockade thermometry

TL;DR

This paper presents a new method for accurate Coulomb blockade thermometry that accounts for bias heating effects, enabling primary thermometry at micro-Kelvin temperatures without prior assumptions.

Contribution

The authors introduce a bias-independent technique to extract electron temperature and charging energy in Coulomb blockade thermometers, improving primary thermometry capabilities.

Findings

High-precision extraction of charging energy without assumptions.

Demonstration of bias voltage effects on electron temperature.

Observation of phonon temperature dependence below 100 mK.

Abstract

Coulomb blockade thermometers (CBTs) are versatile and, in principle, primary thermometers operating down to the micro-Kelvin range but bias heating spoils the thermometry and the primary mode. Here, we introduce a method to extract the CBT electron temperature in the presence of heat created by an arbitrary bias voltage, and without assumptions on the heat flow mechanisms. The charging energy is extracted with high precision and without any other knowledge, thus making true primary thermometry possible. The experiment also reveals a subtle dependence of the charging energy on phonon temperature below 100 mK likely due to the amorphous AlO$_x$ tunnel junctions.