New Universality at the Magnetic Field Driven Insulator to Integer Quantum Hall Effect Transitions

Abstract

We present a magnetotransport study of a disordered two-dimensional hole system in a strained Ge quantum well. As the magnetic field is increased, a clear transition from a low magnetic field insulator to the $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ quantum Hall state at the lowest density range (controlled by a gate), and to the $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$ state at higher densities, is observed. We find that these transitions are characterized by a new universality: At the critical point, the diagonal and Hall resistivities are equal, within experimental uncertainty. These results are in conflict with the ``floating'' scenario suggested by Khmel'nitzkii [JETP Lett. 38, 552 (1983)] and Laughlin [Phys. Rev. Lett. 52, 2304 (1984)].