TOPOLOGICAL DEFECTS, ORIENTATIONAL ORDER, AND DEPINNING OF THE ELECTRON-SOLID IN A RANDOM POTENTIAL

We report on the results of molecular-dynamics simulation studies of t he classical two-dimensional electron crystal in the presence of disor der. Our study is motivated by recent experiments on this system in mo dulation-doped semiconductor systems in very strong magnetic fields, w here the magnetic length is much smaller than the average interelectro n spacing a(0), as well as by recent studies of electrons on the surfa ce of helium. We investigate the low-temperature state of this system using a simulated-annealing method. We find that the low-temperature s tate of the system always has isolated dislocations, even at the weake st disorder levels investigated. We also find evidence for a transitio n from a hexatic glass to an isotropic glass as the disorder is increa sed. The former is characterized by quasi-long-range orientational ord er, and the absence of disclination defects in the low-temperature sta te, and the latter by short-range orientational order and the presence of these defects. The threshold electric field is also studied as a f unction of the disorder strength, and is shown to have a characteristi c signature of the transition. Finally, the qualitative behavior of th e electron how in the depinned state is shown to change continuously f rom an elastic how to a channel-like, plastic how as the disorder stre ngth is increased.