Phase diagram of second layer of helium adsorbed on graphite

TL;DR

This paper uses advanced simulations to map the phase diagram of the second helium layer on graphite, identifying various phases and their transitions, with results aligning well with experimental data.

Contribution

It provides a detailed phase diagram of second-layer helium on graphite using realistic interactions and path integral Monte Carlo, highlighting phase boundaries and coexistence regions.

Findings

Identification of gas, superfluid, commensurate-solid, and incommensurate-solid phases.

Good agreement of phase boundaries and specific heat with experiments.

Explanation of superfluidity changes through coexistence phase growth.

Abstract

Using realistic helium-helium and helium-graphite interactions and the path integral Monte Carlo method, we are able to identify the gas, superfluid liquid, commensurate-solid, and incommensurate-solid phases, and the coexistence regions between them, for the second layer of helium on graphite. The phase boundaries and the specific heat that we determine are in good agreement with experiment. The appearance and disappearance of superfluidity with increasing coverage can be explained by the growth of coexistence phases, as was observed by torsional oscillator experiments.