Melting transition of two-dimensional crystals

Abstract

The solid-liquid phase transition (PT) in two-dimensional crystals is studied under the assumption that it is driven by the dissociation of elastic dipoles. It is shown that this PT is of first-order and corresponds to a dissociation transition of elastic dipoles. For systems where, via thermal nucleation metastable polycrystalline states are possible besides elastic-dipole formation, a more-complex phase diagram is postulated with lines of first- and second-order PT. In the light of these concepts molecular-dynamics experiments with long- and short-range interactions in two and three dimensions are discussed. Solid-liquid PT observed in various experimental monolayer systems and showing first- and second-order PT are interpreted in terms of the theory developed.