Colossal negative magnetoresistance and the associated field-inducedinsulator-to-metal transition—the most characteristic features of magnetic semiconductors—are observed in n-type rare-earth oxides1 and chalcogenides2, p-type manganites3 and n-type4, 5 and p-type diluted magnetic semiconductors4, 6, as well as in quantum wells of n-type diluted magnetic semiconductors7, 8, 9. Here, we report on magnetotransport studies of Mn-modulation-doped InAs quantum wells, which reveal an insulator-to-metal transition that is driven by a magnetic field and dependent on bias voltage, with abrupt and hysteretic changes of resistance over several orders of magnitude. These phenomena coexist with the quantized Hall effect in high magnetic fields. We show that the exchange coupling between a hole and the parent Mn acceptor produces a magnetic anisotropy barrier that shifts the spin relaxation time of the bound hole to a 100 s range in compressively strained quantum wells. This bistability of the individual Mn acceptors explains the hysteretic behaviour while opening prospects for information storing and processing. At high bias voltage another bistability, caused by the overheating of electrons10, gives rise to abrupt resistance jumps.
At a glance
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