Phase Diagram of Second Layer ofH4eAdsorbed on Graphite

Abstract

Using realistic helium-helium and helium-graphite interactions and the path integral Monte Carlo method, we are able to identify gas, superfluid liquid, commensurate-solid, and incommensurate-solid phases, and the coexistence regions between them, for the second layer of ${}^4\mathrm{He}$ on graphite. The phase boundaries and the specific heat 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.