Electronic and optical properties of ferromagnetic GaMnAs in a multi-band tight-binding approach

TL;DR

This study compares two tight-binding models to analyze the electronic and optical properties of ferromagnetic GaMnAs, revealing significant differences in localization and optical conductivity predictions, with implications for understanding impurity effects.

Contribution

It provides a detailed comparison of two realistic tight-binding models for GaMnAs, highlighting their differing predictions for electronic structure and optical properties at various impurity concentrations.

Findings

Masek's model shows small deviations from p-doped GaAs at low impurity levels.

Tang and Flatte's model predicts impurity-band formation at low concentrations.

At higher concentrations, models diverge in localization and optical conductivity predictions.

Abstract

We consider the electronic properties of ferromagnetic bulk GaMnAs at zero temperature using two realistic tight-binding models, one due to Tang and Flatte and one due to Masek. In particular, we study the density of states, the Fermi energy, the inverse participation ratio, and the optical conductivity with varying impurity concentration x=0.01-0.15. The results are very sensitive to the assumptions made for the on-site and hopping matrix elements of the Mn impurities. For low concentrations, x<0.02, Masek's model shows only small deviations from the case of p-doped GaAs with increased number of holes while within Tang and Flatte's model an impurity-band forms. For higher concentrations x, Masek's model shows minor quantitative changes in the properties we studied while the results of the Tang and Flatte model exhibit qualitative changes including strong localization of eigenstates with energies close to the band edge. These differences between the two approaches are in particular visible in the optical conductivity, where Masek's model shows a Drude peak at zero frequency while no such peak is observed in Tang and Flatte's model. Interestingly, although the two models differ qualitatively the calculated effective optical masses of both models are similar within the range of 0.4-1.0 of the free electron mass.