Melting of a quasi-two-dimensional metallic system.

We analyze the melting of a quasi-two-dimensional metallic system using the results of a series of Monte Carlo simulations of an array of Pb atoms. The system was chosen to model the melting behavior observed for the monolayer of Pb that segregates in the liquid-vapor interface of a dilute Pb in Ga alloy [B. Yang et al., Proc. Natl. Acad. Sci. USA 96, 13 009 (1999)]. Our calculations employed a realistic pair interaction potential between lead pseudoatoms, one that is known to describe accurately the properties of the three-dimensional metal near the melting point. Our results reveal that in the quasi-two-dimensional Pb system melting is a two-stage process which proceeds through formation of a stable intermediate hexatic phase, in agreement with the prediction of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. Both the solid-to-hexatic and the hexatic-to-liquid transitions are found to be first order in our simulations.