Second harmonic AC calorimetry technique within a diamond anvil cell

TL;DR

This paper introduces a novel second harmonic AC calorimetry method for measuring specific heat within diamond anvil cells, enabling high-pressure studies of materials' thermodynamic properties with broad compatibility.

Contribution

The authors developed a new, DAC-independent calorimetry technique that allows specific heat measurements at high pressures, demonstrated on MgB2 superconductor.

Findings

Detected a clear specific heat anomaly at Tc in MgB2

Technique is compatible with existing high-pressure resistance measurements

Allows measurements at higher pressures than previous methods

Abstract

Tuning the energy density of matter at high pressures gives rise to exotic and often unprecedented properties, e.g., structural transitions, insulator-metal transitions, valence fluctuations, topological order, and the emergence of superconductivity. The study of specific heat has long been used to characterize these kinds of transitions, but their application to the diamond anvil cell (DAC) environment has proved challenging. Limited work has been done on the measurement of specific heat within DACs, in part due to the difficult experimental setup. To this end we have developed a novel method for the measurement of specific heat within a DAC that is independent of the DAC design and therefore readily compatible with any DACs already performing high pressure resistance measurements. As a proof-of-concept, specific heat measurements of the MgB2 superconductor were performed, showing a clear anomaly at the transition temperature (Tc), indicative of bulk superconductivity. This technique allows for specific heat measurements at higher pressure than previously possible.