FLOATING UP OF THE EXTENDED STATES OF LANDAU-LEVELS IN A 2-DIMENSIONAL ELECTRON-GAS IN SILICON MOSFETS

Phase diagram in H, N(s) plane for a 21) electron gas in Si MOSFET's h as been studied. It was found that transition to a low-electron-densit y insulating phase occurs only if all the extended states have passed, leaving Fermi sea through the Fermi level. In contrast to the case of high magnetic fields. when the extended states of each Landau level f ollow its center, in weak magnetic fields they float up and finally co mbine upon lowering the magnetic field.