METAL-INSULATOR-TRANSITION IN SI INVERSION-LAYERS IN THE EXTREME QUANTUM LIMIT

We report magnetotransport data of an insulating phase in silicon inversion layers in the extreme quantum limit at a Landau-level filling factor of nu less than or similar 1/2. The transport properties have proved to be unexpectedly similar to those of the insulating phase in GaAs/AlxGa1-xAs heterostructures around nu = 1/5 (for electron gas) and nu = 1/3 (for hole gas) where magnetically induced Wigner solid formation has been reported. Strongly nonlinear current-voltage characteristics display threshold behavior and tend to saturate as current increases. The similarity of transport properties might strongly suggest the formation of a pinned electron solid in Si inversion layers at nu less than or similar 1/2. However, in the presence of long-range potential, at nu = 1/2 the percolation metal-insulator transition is expected. Both the magnetically induced electron solid formation and the percolation transition are considered as possible explanations of the observed effects.