2 DIFFERENT REGIMES OF ELECTRON-TRANSPORT IN A 2-DIMENSIONAL ELECTRON-GAS AT HIGH MAGNETIC-FIELDS

We demonstrate experimentally the existence of two different regimes o f electron transport in the transition regions between Hall plateaus a t high magnetic fields. One regime is found in the high-magnetic-field tail of a Shubnikov-de Haas peak, while the other one is in the remai ning magnetic-field region of the peak. The magnetoresistance measured in the two regimes is shown to arise from different physical origins. The experiment supports the recent theory that predicts the existence of a percolating metallic electron system at high magnetic fields.