Unveiling the impurity band inducing ferromagnetism in magnetic semiconductor (Ga,Mn)As

TL;DR

This study uses soft x-ray ARPES to identify the impurity band responsible for ferromagnetism in (Ga,Mn)As, clarifying the long-standing debate on its electronic structure and the role of hole transport in the impurity band.

Contribution

It provides direct experimental evidence of the Mn 3d-derived impurity band and its hybridization with the host valence band, resolving a decade-long controversy.

Findings

Identification of the impurity band as a split-off Mn-impurity state

Impurity band hybridized with light-hole band of GaAs

Hole transport in the impurity band causes ferromagnetism

Abstract

(Ga,Mn)As is a paradigm diluted magnetic semiconductor which shows ferromagnetism induced by doped hole carriers. With a few controversial models emerged from numerous experimental and theoretical studies, the mechanism of the ferromagnetism in (Ga,Mn)As still remains a puzzling enigma. In this Letter, we use soft x-ray angle-resolved photoemission spectroscopy to positively identify the ferromagnetic Mn 3d-derived impurity band in (Ga,Mn)As. The band appears hybridized with the light-hole band of the host GaAs. These findings conclude the picture of the valence band structure of (Ga,Mn)As disputed for more than a decade. The non-dispersive character of the IB and its location in vicinity of the valence-band maximum indicate that the Mn 3d-derived impurity band is formed as a split-off Mn-impurity state predicted by the Anderson impurity model. Responsible for the ferromagnetism in (Ga,Mn)As is the transport of hole carriers in the impurity band.