We investigate the first layer of helium adsorbed on graphite with path-integral Monte Carlo, examining the role of substrate corrugations on the phase diagram. When no corrugations are present, the equilibrium state of the system is a liquid phase, with solidification occurring only under compression but before layer promotion. We determine the solid-liquid coexistence region and compare our results to recent Green’s-function Monte Carlo calculations on the same system. When substrate corrugations are included, we find that the equilibrium phase is the $\sqrt{3}\times \sqrt{3}$ commensurate solid phase that is well known from experiment. The melting behavior, heat capacity, and single-particle binding energy are determined and compared to experiment. We further find that for densities below the commensurate coverage, the low-temperature phase of the system consists of solid clusters in coexistence with coalesced vacancies. We find no first-layer liquid phase and so no superfluidity in this layer, in contrast to some rather recent suggestions.

• Received 23 November 1999

DOI:https://doi.org/10.1103/PhysRevB.62.5228