Metallic conductivity near the metal-insulator transition

C. Leighton, I. Terry, P. Becla

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The low-temperature transport properties of the diluted magnetic semiconductor (Formula presented) (or In, Al) have been studied on the metallic side of the metal-insulator transition (MIT). The critical region near the MIT has been probed by utilizing the persistent photoconductivity effect displayed by this material. This has allowed us to study the MIT in a single sample of this magnetic semiconductor in zero magnetic field. The critical behavior is consistent with the predictions of the scaling theory of electron localization with a conductivity critical exponent close to 1.0. The critical carrier density is determined to be (Formula presented) for (Formula presented) The temperature dependence of the metallic conductivity in the critical region (below 1 K) is well described by a theory that takes into account the effects of (Formula presented) interactions and weak localization. The transport properties of (Formula presented) and (Formula presented) Al have been studied in the weakly localized regime. At low temperatures the samples with low Mn content (Formula presented) display a rapid decrease of the conductivity below a certain temperature. This effect (which has previously been observed in (Formula presented) is due to the scattering of electrons by bound magnetic polarons (BMP’s) formed on quasilocalized s spins. However, in samples with higher x, we observe no evidence for this form of scattering. We propose that such an effect is only observable in the paramagnetic phase, whereas, in the presence of spin-glass order, the temperature dependence of the BMP scattering process is weak enough to be masked by other electron scattering mechanisms.

Original languageEnglish (US)
Pages (from-to)9773-9782
Number of pages10
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number15
StatePublished - Jan 1 1998

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