Reentrant melting in solid films with quenched random impurities

Crystalline films with a quenched distribution of impurities are studied. These materials are stable only over a finite band of temperatures. At sufficiently low temperatures, thermally excited dislocation pairs are broken apart by the random impurity potential. The hexatic phase which results can persist down to T = 0. For large impurity concentrations, the solid phase is destroyed entirely. These conclusions are consistent with recent studies of vibrating binary ball-bearing arrays, and could be tested experimentally in a variety of other systems with quenched disorder.