WIGNER SOLID IN 2-DIMENSIONAL ELECTRON-SYSTEM IN SILICON IN THE EXTREME QUANTUM LIMIT

The metal-insulator transition in a 2D electron gas of Si MOSFETs has been investigated. In the extreme quantum limit, the phase boundary in the H, N(s) plane has been found to be a straight line with the slope nu(c) = 0.53 +/- 0.01. Transport properties of the insulating phase have proven to be unexpectedly similar to those of the insulating phase in GaAs/AlGaAs heterostructures where magnetically induced Wigner solid formation has been reported. Strongly nonlinear current-voltage characteristics with linear V(I) dependence below some threshold voltage, V(c), and saturation at V > V(c) were observed. The longitudinal resistance corresponding to the linear part of the I-V characteristics demonstrates an activated temperature.dependence. Knowing the values of the threshold voltage and activation energy we obtain a characteristic length that is large compared to the distance between electrons, which excludes a single-electron picture of nonlinearity. The similarity of transport properties strongly suggests the same physical nature of the insulating phases in Si inversion layers and GaAs/AlGaAs heterostructures. However, the value of nu(c) is somewhat surprising since, in the presence of a long-range potential, the percolation metal-insulator transition is expected at precisely this filling factor. The percolation transition is considered as an alternative explanation of the observed effects.