"Magnetically dead" surface layers on ferromagnetic semiconductors

We perform an exact model calculation for the conduction-band spin structure of ferromagnetic semiconductors. The purpose of this illustrative quasiatomic theory (which is an abstraction of our earlier general theory) is to demonstrate that the case $T=0\mathrm{}$ (i.e., ferromagnetic saturation) exhibits vanishingly small spectral weights of certain quasiparticle or scattering states which, however, become manifest for $T>\mathrm{}0\mathrm{}$, and determine the electron-spin polarization. Hence $T=0\mathrm{}$ results cannot be generalized to nonzero temperatures and should not be used to prove or disprove the existence of "magnetically dead" surface layers on ferromagnetic semiconductors. The existence of such dead layers has frequently been postulated to explain the electron-spin polarization in photoemission and field-emission experiments.