Observation of magnetic-field-induced delocalization: Transition from Anderson insulator to quantum Hall conductor

We report the first experimental observation of a magnetic-field-induced transition from an Anderson insulator to a quantum Hall conductor in a two-dimensional electron gas (2DEG) system. With sufficiently strong disorder, the 2DEG is an Anderson insulator with a divergent resistance at B=0. The 2DEG is transformed into a quantum Hall conductor with a vanishing resistance as T→0 and a quantized Hall resistance when the lowest Landau level is filled. The observations demonstrate the magnetic-field-induced delocalization and are consistent with a recently proposed global phase diagram.