Metal-insulator transition induced by fluctuations of the magnetic potential in semiconductors with magnetic impurities

Abstract: We investigate the metal-insulator transition occurring in semiconductors with magnetic impurities when lowering temperature. In contrast to the usually considered percolation transition in the non-uniform medium induced by the localization of charge carriers in the fluctuating \emph{electric} potential, the studied transition is connected with their localization in the fluctuating \emph{magnetic} potential produced by magnetized impurities (more accurately - in the combined fluctuating potential). When decreasing temperature, the magnetization of magnetic impurities in the semiconductor becomes higher and even at the invariable (temperature independent) amplitude of the electric potential, the magnetic component of the total potential increases. With increasing fluctuation amplitude, the Fermi level of charge carriers sinks deeper and deeper into the growing tail of density of states until it falls under the percolation level. For that, fluctuations of the total potential have to run up to some critical value. On reaching that value, the transition occurs from the metal conductivity to the activation one (the metal-insulator transition).