A Simple Experimental Setup for Simultaneous Superfluid-response and Heat-capacity Measurements for Helium in Confined Geometries

TL;DR

This paper presents a simple, integrated method to simultaneously measure superfluid response and heat capacity of helium in confined geometries using a torsional oscillator setup, enabling direct comparison of thermodynamic properties.

Contribution

The authors developed a straightforward approach to incorporate heat capacity measurements into an existing torsional oscillator without modifications, allowing simultaneous, accurate data collection on helium samples.

Findings

Successful simultaneous TO and HC measurements down to 30 mK.

Reproduced previous results with high accuracy.

Method applicable to various experiments requiring direct comparison.

Abstract

Torsional oscillator (TO) is an experimental technique which is widely used to investigate superfluid responses in helium systems confined in porous materials or adsorbed on substrates. In these systems, heat capacity (HC) is also an important quantity to study the local thermodynamic properties. We have developed a simple method to incorporate the capability of HC measurement into an existing TO without modifying the TO itself. By inserting a rigid thermal isolation support made of alumina and a weak thermal link made of fine copper wires between a standard TO and the mixing chamber of a dilution refrigerator in parallel, we were able to carry out simultaneous TO and HC measurements on exactly the same helium sample, i.e., four atomic layers of $^4$He adsorbed on graphite, with good accuracies down to 30 mK. The data reproduced very well the previous workers' results obtained independently using setups optimized for individual measurements. This method is conveniently applicable to a variety of experiments where careful comparisons between results of TO and HC measurements are crucial. We describe how to design the thermal isolation support and the weak thermal link to manage conflicting requirements in the two techniques.