Phase Boundaries between Quantum Hall Metaland Hall Insulator in Si-MOSFET's and Many-Body Enhancementof Valley- and Zeeman-Splitting

Abstract

We have experimentally studied metal-insulator transitions in a two-dimensional electron system in Si-MOSFET's in a magnetic field and derived a phase diagram on aν (Landau level filling factor) vs. disorder (resistivity in the absence of magnetic field)plane. Structures of stabilized phase boundaries at ν =1 and ν =2 are discussed based on many-body enhancement of valley- and Zeeman-splitting, respectively.