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\title{The Role of Substrate Corrugation in Helium Monolayer Solidification}
\author{M. E. Pierce and E. Manousakis}
\address{
Department of Physics and Center for Materials Research and Technology,
Florida State University, Tallahassee, FL 32306-4350
}
\date{\today}
\maketitle
\begin{abstract}
\noindent
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 occuring 
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 $\sqrt 3 \times \sqrt3$ 
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.  
\end{abstract}
\pacs{PACS numbers 67.70.+n, 67.40 Kh}
] 

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