The Mobility Edge in Disordered Ferromagnetic Doped Semiconductors

While the clearest example of ferromagnetism in doped semiconductors is seen in diluted magnetic semiconductors such as Ga$_{1-x}$Mn$_x$As,\footnote{H. Ohno, Science 281, 951 (1998)} under certain conditions, semiconductors doped with non-magnetic impurities may also exhibit ferromagnetic ground states.\footnote{Erik Nielsen and R. N. Bhatt, APS March Meeting 2006.} We present numerical results of the nature of single particle states in such a positionally disordered three-dimensional system with a maximally spin-polarized ground state using a realistic potential for hydrogenic centers.\footnote{R. N. Bhatt and T. M. Rice, Physical Review B 23, 1920 (1981).} In particular, we identify the mobility edges, which mark the energies at which single particle states become delocalized, and whose location relative to the Fermi energy determine electronic transport in the system. We describe the dependence of the mobility edges on impurity density and potential, and discuss the variation of conductivity with impurity and carrier density.