THE METALLICLIKE CONDUCTIVITY OF A 2-DIMENSIONAL HOLE SYSTEM

We report on a zero magnetic field transport study of a two-dimensiona l, variable-density, hole system in GaAs, As the density is varied we observe, for the first time in GaAs-based materials, a crossover from an insulating behavior at low density, to a metalliclike behavior at h igh density, where the metallic behavior is characterized by a large d rop in the resistivity as the temperature is lowered. These results ar e in agreement with recent experiments on Si-based two-dimensional sys tems. We show that, in the metallic region, the resistivity is dominat ed by an exponential temperature dependence with a characteristic temp erature which is proportional to the hole density.