Infrared conductivity of metallic (III,Mn)V ferromagnets

TL;DR

This paper develops a theoretical model for the infrared optical properties of metallic (III,Mn)V ferromagnetic semiconductors, highlighting inter-valence-band transitions and proposing a method to accurately determine free carrier density despite experimental challenges.

Contribution

It introduces a theory for infrared conductivity in (III,Mn)V ferromagnets and suggests using transverse f-sum rule measurements to accurately measure free carrier density.

Findings

Conductivity peaks at ~220 meV due to inter-valence-band transitions.

Broadening of the Drude peak obscured by these transitions.

Transverse f-sum rule can accurately determine free carrier density.

Abstract

We present a theory of the infrared conductivity and absorption coefficients of metallic (III,Mn)V ferromagnetic semiconductors. We find that the conductivity is dominated by inter-valence-band transitions that produce peaks at $\hbar \omega \sim 220 {\rm meV}$ and obscure the broadened Drude peak. We demonstrate that transverse f-sum rule measurements can be used to extract accurate values for the free carrier density, bypassing the severe characterization difficulties that have till now been created by the large anomalous Hall effect in these materials.