Magnetic hard gap due to bound magnetic polarons in the localized regime

Gaurab Rimal,Jinke Tang

doi:10.1038/srep42224

Abstract

We investigate the low temperature electron transport properties of manganese doped lead sulfide films. The system shows variable range hopping at low temperatures that crosses over into an activation regime at even lower temperatures. This crossover is destroyed by an applied magnetic field which suggests a magnetic origin of the hard gap, associated with bound magnetic polarons. Even though the gap forms around the superconducting transition temperature of lead, we do not find evidence of this being due to insulator-superconductor transition. Comparison with undoped PbS films, which do not show the activated transport behavior, suggests that bound magnetic polarons create the hard gap in the system that can be closed by magnetic fields.

Highlights

Metal-insulator transitions (MIT) due to disorder or electron-electron interaction have been at the center of condensed matter physics research
We study the low temperature magnetotransport properties of Mn doped PbS (MnPbS), which shows the crossover from Efros and Shklovskii (ES) variable range hopping (VRH) to activated transport behavior at low temperature
Pb impurity peaks were seen in X-ray diffraction (XRD) which should exist as metallic clusters

Summary

Introduction

Metal-insulator transitions (MIT) due to disorder or electron-electron interaction have been at the center of condensed matter physics research. Depending on the mechanisms of the HG formation, low temperature measurements may or may not reveal the crossover from ES VRH hopping to transport of activation type[7,13,14]. In strongly localized diluted magnetic semiconductors (DMS), the spins from the localized states may exchange couple to and align the spins of the transition metal dopants that can lead to the formation of a bound magnetic polaron (BMP)[15,16,17,18]. The transport of BMP typically follows VRH, sometimes with modification[22] It was argued[7] that adding a bare electron to the system costs the energy of spin relaxation due to the formation of BMP at the final site of the hop. A sign reversal in the exciton g-factor with increasing Mn concentration has been inferred based on low Mn concentration data[30]

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Results

Conclusion