MAGNETIC-FIELD-INDUCED ANOMALOUS PHASE-TRANSITIONS IN P-SIGE SI HETEROSTRUCTURES/

We present the low-temperature magneto-transport measurements on a two -dimensional hole gas in the p-type modulation doped SiGe alloy confin ed by an Si barrier. We observe a magnetic-field-induced transition wh ich occurs at high magnetic fields from an integer quantum Hall phase to a Hall insulator phase :and finally reenters to a nu = 1 integer qu antum Hall phase. This Hall insulator is centred at nu = 1.5 which is unanticipated by the global phase diagram. Scaling analysis and univer sal phenomena are found to be different at the two transition points. These results are attributed to the unusual energy level scheme in p-S iGe.