"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures - art. no. 161308

We show that in dilute metallic p-SiGe heterostructures, magnetic field can cause multiple quantum Hall-insulator-quantum Hall transitions. The insula ting states are observed between quantum Hall states with filling factors v = 1 and 2 and, to the best of our knowledge for the first time, between v= 2 and 3 and between v = 4 and 6. The latter are in contradiction with the original global phase diagram for the quantum Hall effect. We suggest that the application of a (perpendicular) magnetic field induces insulating beha vior in metallic p-SiGe hetero structures in the same way as in Si metal-ox ide-semiconductor field-effect transistors (MOSFETs). This insulator is the n in competition with, and interrupted by, integer quantum Hall states lead ing to the multiple re-entrant transitions. The phase diagram which account s for these transitions is similar to that previously obtained in Si MOSFET s thus confirming its universal character.