Monte Carlo studies of two-dimensional phases of helium using a shadow wave function

The solid and liquid phases of two-dimensional He-4 are studied in detail u sing a variational "shadow" wave function. This wave function provides a un ified description of both phases; spontaneous crystallization from a disord ered initial state occurs in the solid phase. We have investigated the prop erties of the solid phase in detail and find that it lacks long range trans lational order, has. a high density of defects, and low angular order relat ive to classical two-dimensional solids. These results are very similar to results obtained from simulations of a quantum hard disk system. We have al so computed these properties for the liquid phase. These properties vary ra pidly in the transition region and serve as a good signal for the transitio n itself.