Specific heat of thin $^4$He films on graphite

TL;DR

This study uses Quantum Monte Carlo simulations to analyze the specific heat of two-layer $^4$He films on graphite, finding results consistent with experiments but not supporting claimed exotic phases, and questioning the interpretative power of heat capacity data.

Contribution

First simulation-based estimation of specific heat in $^4$He films on graphite, challenging claims of supersolid and superfluid hexatic phases based on heat capacity.

Findings

Results align with experimental data but do not show exotic phases.

Heat capacity alone may be insufficient to identify structural or superfluid transitions.

Simulations suggest reinterpretation of experimental phase claims.

Abstract

The specific heat of a two-layer He-4 film adsorbed on a graphite substrate is estimated as a function of temperature by Quantum Monte Carlo simulations. The results are consistent with recent experimental observations, in that they broadly reproduce their most important features. However, neither the "supersolid" nor the "superfluid hexatic" phases, of which experimental data are claimed to be evidence, are observed. It is contended that heat capacity measurements alone may not be a good predictor of structural and superfluid transitions in this system, as their interpretation is often ambiguous.