Electronic quasiparticle spectrum of ferromagnetic semiconductors in the sf model

Publisher Website
Google Scholar
Abstract
The sf model for ferromagnetic semiconductors-Coulomb interaction included, but with simplified f-f exchange-has been exactly solved in the limit W to 0 (W=band width) using a Green function technique. It turns out that the original s level is split by the sf interaction into six quasiparticle levels for each electron spin direction. Starting from the atomic limit, a calculation has been performed for a conduction band of finite width under the assumption that it contains only one electron. The temperature behaviour of the quasiparticles energies and their spectral weights (reduced densities of states) is discussed. It is shown that especially very near to the ferromagnetic saturation, the dependence of the spectral weights on the magnetisation of the localised f system gives rise to a spectacular redistribution of the density of states. Furthermore, for sf coupling constants g up to 1 eV, a small variation of g leads already to very strong shifts in weight between the different quasiparticle subbands. It turns out that the usual assumption that the conduction band is split into two spin-polarised subbands is only reasonable, if at all, for very small g values.