Percolation Metal-Insulator Transitions in the Two-Dimensional Electron System of AlGaAs/GaAs Heterostructures

We investigate the transport properties of insulating phases in the 2D electron system of high-mobility AlGaAs/GaAs heterostructures of Corbino geometry at very low temperatures. We find that the nonlinear current-voltage characteristics for insulating phases in the integer and fractional quantum Hall regime and for a low-density insulating phase are very similar. The behavior of these characteristics with changing temperature and filling factor unambiguously points to the percolation metal-insulator transition as the cause for all insulating phases investigated. We propose a metal-insulator phase diagram in the ($B,N_s$) plane based on our experimental data.