Electron correlations in Mn$_x$Ga$_{1-x}$As as seen by resonant electron spectroscopy and dynamical mean field theory

TL;DR

This study combines resonant photo-emission experiments with LDA+DMFT calculations to clarify the electronic structure of Mn-doped GaAs, revealing broad Mn states and the absence of an impurity band, thus shedding light on its ferromagnetism.

Contribution

It provides a combined experimental and theoretical analysis showing the importance of correlation effects in Mn-doped GaAs's electronic structure.

Findings

Mn states extend over a broad energy range including the valence band top

No impurity band splits off from the valence band edge

Holes are primarily localized around Mn impurities

Abstract

After two decades from the discovery of ferromagnetism in Mn-doped GaAs, its origin is still debated, and many doubts are related to the electronic structure. Here we report an experimental and theoretical study of the valence electron spectrum of Mn-doped GaAs. The experimental data are obtained through the differences between off- and on-resonance photo-emission data. The theoretical spectrum is calculated by means of a combination of density-functional theory in the local density approximation and dynamical mean-field theory (LDA+DMFT), using exact diagonalisation as impurity solver. Theory is found to accurately reproduce measured data, and illustrates the importance of correlation effects. Our results demonstrate that the Mn states extend over a broad range of energy, including the top of the valence band, and that no impurity band splits off from the valence band edge, while the induced holes seem located primarily around the Mn impurity.