The formation of disordered regions is observed on the Ga(111)c2×8 surface, at temperatures in the range 150–350 °C. The disorder occurs by the diffusion of surface adatoms in the 〈011¯〉 directions. The disordered regions form at domain boundaries, and grow continuously with temperature until the entire surface becomes disordered at 300 °C. We argue that this phase transition is an example of premelting in two dimensions, i.e., ‘‘edge melting.’’

• Received 20 March 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.3257