Magnetic circular dichroism in GaMnAs: (no) evidence for an impurity band

TL;DR

This study uses a multi-band tight-binding model to analyze the magneto-optical properties of GaMnAs, showing that positive magnetic circular dichroism does not conclusively indicate the presence of an impurity band.

Contribution

It compares models with and without an impurity band, demonstrating that positive MCD signals are not definitive evidence for impurity bands in GaMnAs.

Findings

Positive MCD observed in both models.

Positive MCD results from antiferromagnetic p-d coupling.

MCD signal alone is inconclusive for impurity band presence.

Abstract

Magneto-optical properties of the ferromagnetic semiconductor GaMnAs are studied in a material specific multi-band tight-binding approach. Two realistic models are compared: one has no impurity band while the other shows an impurity band for low Mn concentrations. The calculated magnetic circular dichroism (MCD) is positive for both models proving that, unlike previously asserted, the observed positive MCD signal is inconclusive as to the presence or absence of an impurity band in GaMnAs. The positive MCD is due to the antiferromagnetic p-d coupling and the transitions into the conduction band.