Reentrant Insulator-Metal-Insulator Transition atB=0in a Two-Dimensional Hole Gas

We report the observation of a reentrant insulator-metal-insulator transition at $B=0\mathrm{}$ in a two-dimensional (2D) hole gas in GaAs at temperatures down to 30 mK. At the lowest carrier densities the holes are strongly localized. As the carrier density is increased a metallic phase forms, with a clear transition at $\sigma \simeq {5e}^2/h$. Further increasing the density weakens the metallic behavior and eventually leads to the formation of a second insulating state for $\sigma \gtrsim {50e}^2/h$. In the limit of high carrier densities, where $k_{F}l$ is large and $r_s$ is small, we thus recover the results of previous work on weakly interacting systems showing the absence of a 2D metallic state.