Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopyElectronic

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronicstructure ofGa1#1;xMnxAsnear the Fermi energy. The band structure of this archetypical dilute-momentferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements ofthe unpolarized infrared absorption and their phenomenological impurity-band interpretation. Unlike theunpolarized absorption, the infrared magneto-optical effects we study are intimately related to ferromag-netism, and their interpretation is much more microscopically constrained in terms of the orbital characterof the relevant band states. We show that the conventional theory of the disordered valence band with anantiferromatnetic exchange term accounts semiquantitatively for the overall characteristics of themeasured infrared magneto-optical spectra.