Anomalous Fermi level behavior in GaMnAs at the onset of ferromagnetism

TL;DR

This study uses resonant tunneling spectroscopy to investigate the Fermi level behavior in GaMnAs, revealing its position in the band gap and its anomalous movement near the onset of ferromagnetism, suggesting impurity band involvement.

Contribution

It provides the first systematic analysis of Fermi level dynamics across various Mn concentrations in GaMnAs, highlighting impurity band effects on ferromagnetism.

Findings

Fermi level remains in the band gap across all Mn concentrations.

Fermi level is closest to the valence band at x=1.0%, near ferromagnetic transition.

Fermi level moves away from the valence band as x deviates from 1.0%.

Abstract

We present the systematic study of the resonant tunneling spectroscopy on a series of ferromagnetic-semiconductor Ga1-xMnxAs with the Mn content x from ~0.01 to 3.2%. The Fermi level of Ga1-xMnxAs exists in the band gap in the whole x region. The Fermi level is closest to the valence band (VB) at x=1.0% corresponding to the onset of ferromagnetism near the metal-insulator transition (MIT), but it moves away from the VB as x increasing or decreasing from 1.0%. This anomalous behavior of the Fermi level indicates that the ferromagnetism and MIT emerge in the Mn-derived impurity band.