Theory of optical conductivity for dilute GaMnAs

TL;DR

This paper develops a semi-microscopic theory for the optical conductivity of dilute GaMnAs, accurately capturing impurity band transitions, the metal-insulator transition, and reproducing experimental optical features.

Contribution

It introduces an effective Hamiltonian derived from microscopic calculations to describe optical properties of dilute GaMnAs, including impurity band effects and transition behaviors.

Findings

Identifies a metal-insulator transition within the impurity band at specific doping levels.

Reproduces the mid-infrared peak and its doping-dependent redshift.

Finds an optical mass close to the electron mass, varying near the transition.

Abstract

We construct a semi-microscopic theory, to describe the optical conductivity of GaMnAs in the dilute limit, x = 1%. We construct an effective Hamiltonian that captures inside-impurity band optical transitions as well as transitions between the valence band and the impurity band. All parameters of the Hamiltonian are computed from microscopic variational calculations. We find a metal-insulator transition within the impurity band in the concentration range, x = 0.2 -0.3 for uncompensated and x = 1-3% for compensated samples, in good agreement with the experiments. We find an optical mass m_opt = m_e, which is almost independent of the impurity concentration excepting in the vicinity of the metal-insulator transition, where it reaches values as large as m_opt = 10 m_e. We also reproduce a mid-infrared peak at \hbar \omega = 200 meV, which redshifts upon doping, in quantitative agreement with the experiments.