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

TL;DR

This paper explores a metal-insulator transition in magnetic impurity semiconductors caused by magnetic potential fluctuations, revealing a transition driven by magnetic, not electric, potential effects as temperature decreases.

Contribution

It introduces a novel mechanism for metal-insulator transition driven by magnetic potential fluctuations, contrasting with traditional electric potential-based percolation models.

Findings

Transition occurs when magnetic potential fluctuations reach a critical level.

Fermi level sinks into the density of states tail due to magnetic fluctuations.

Transition from metallic to activated conduction at critical fluctuation amplitude.

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).