Theory of Magnetically Assisted indirect Transitions in Magnetic Semiconductors

Abstract

The optical absorption coefficient for ferromagnetic semiconductors has been calculated for an indirect transition in which spin-fluctuation scattering takes the place of the usual phonon scattering. The resulting absorption coefficient is found to be proportional to $〈{\left|S_{{\overrightarrow{\mathrm{Q}}}_Z}\right|}^2〉$, where $\overrightarrow{\mathrm{Q}}$ is the wave-vector difference between the valence-band maximum and the conduction-band minimum. The fact that this decreases with decreasing temperature below the Curie point can lead to an apparent blue shift of the absorption edge similar to what is observed in Cd${\mathrm{Cr}}_2$ ${\mathrm{S}}_4$.