Annotation

V.D.Lakhno, E.L.Nagaev.
The dielectric constant of magnetic semiconductors //Zh. Eksp. Teor. Fiz., 1979, v.77, №4, p.1407-1416

      The magnetization dependence of the dielectric constant е(w,q) of a ferromagnetic semiconductor is calculated. Since the semiconductor gap narrows rapidly with increasing magnetization, е(w,q) may increase considerably as the temperature is lowered or on the application of a strong enough external magnetic field. This entails a number of physical consequences (the possibility of an insulator-metal phase transition in donor-doped crystals, etc.). The light absorption coefficient in the spin-wave region is calculated. The temperature dependence of the absorption coefficient indicates that an electron that appears in the conduction band as a result of interaction with light is not bare, but is dressed because of its interaction with magnons. Thus, the Franck-Condon principle, according to which there should be no change in the state of the magnetic subsystem when an electron goes from the valence band to the conduction band, turns out to be violated in this case.