QUASI-PARTICLES IN CALCIUM-DOPED YTTRIUM-IRON GARNETS

In yttrium-iron garnets an electrical charge is carried by quasipartic les based on compensating holes which move either at oxygen or iron io ns of the tetragonal sublattice. The quasiparticles can also get local ized because of their coupling to optical phonons on the iron sites. A multi-band model of holes coupled to phonons is applied to find addit ional energy levels in the gap between the lower of the narrow 3d band s and the wide 2p band, whose occurrence plays a crucial role in a con ductivity mechanism. The density of states is considerably modified by the interaction between the holes and local distortion of the lattice .