Grain formation, stringlike collective motion, and the onset of diffusion in disordered two-dimensional crystals

Two-dimensional crystals in random potentials are studied by molecular-dynamics methods. The ground state of the system is characterized by a transition of the random-potential-induced defect configurations, which evolve from a dilute gaslike state at weak random potentials to a grain-boundary state at strong random potentials. The dynamics of the system is strongly affected by the defect structure. Stringlike collective hopping of particles …