Light-induced melting of colloidal crystals in two dimensions

We demonstrate that particles confined to two dimensions (2D) and subjected to a one-dimensional (1D) periodic potential exhibit a rich phase diagram, with both "locked floating solids" and smectic phases. The resulting phase s and phase transitions are studied as a function of temperature and potent ial strength. We find rerntrant melting as a function of the potential stre ngth. Our results lead to universal predictions consistent with recent expe riments on 2D colloids in the presence of a laser-induced 1D periodic poten tial.