OBSERVATION OF A 2-STAGE MELTING TRANSITION IN 2 DIMENSIONS

We have performed hybrid Monte Carlo and molecular dynamics computer s imulations to study the melting transition for a two-dimensional mater ial consisting of classical point particles interacting via an r(-12) repulsive pair potential. As the density increases, the Liquid phase d evelops hexatic structure at values of the pressure that are too low t o allow coexistence with a stable crystal possessing an equilibrium co ncentration of vacancies. Bond orientational order, translational orde r, and densities are computed for sub-blocks of the total system. Hist ograms of these quantities remain unimodal throughout the transition r egion, indicating no tendency for phase separation. Through the use of block analysis techniques, we extract exponents for the bond orientat ional and translational correlations in the hexatic and the solid that are consistent with the predictions of the Kosterlitz-Thouless-Halper in-Nelson-Young theory.