Precise Calorimetry of Small Metal Samples Using Noise Thermometry

TL;DR

This paper introduces a compact, highly precise calorimeter for small metal samples at ultra-low temperatures, capable of operating in magnetic fields and covering a broad temperature range with minimal heat capacity addendum.

Contribution

It presents a novel calorimeter design utilizing a noise thermometer for accurate, wide-range temperature measurement and effective thermalization techniques for small metal samples in magnetic fields.

Findings

Achieved temperature measurement from 175 μK to 90 mK with high precision.

Demonstrated calorimeter performance on YbRh2Si2, a heavy Fermion metal.

Reduced parasitic heat leaks to tens of femtowatts.

Abstract

We describe a compact calorimeter that opens ultra-low temperature heat capacity studies of small metal crystals in moderate magnetic fields. The performance is demonstrated on the canonical heavy Fermion metal YbRh2Si2. Thermometry is provided by a fast current sensing noise thermometer. This single thermometer enables us to cover a wide temperature range of interest from 175 $\mu$K to 90 mK with temperature independent relative precision. Temperatures are tied to the international temperature scale with a single point calibration. A superconducting solenoid surrounding the cell provides the sample field for tuning its properties and operates a superconducting heat switch. Both adiabatic and relaxation calorimetry techniques, as well as magnetic field sweeps, are employed. The design of the calorimeter results in an addendum heat capacity which is negligible for the study reported. The keys to sample and thermometer thermalisation are the lack of dissipation in the temperature measurement and the steps taken to reduce the parasitic heat leak into the cell to the tens of fW level.