Theoretical Study on multi-band effect on the ferromagnetism of itinerant electrons

点击翻译按钮获取中文摘要

1. We studied the 1D Hubbard model with two-fold orbital degeneracy by using density matrix renormalization group method, and obtained ground state phase diagram. We obtained perfectly ferromagnetic ground state for n<1, n=1 and n>1 where n denotes the electron density per site. The ferromagnetism for n<1 was shown to be fragile against chay the band dispersion, while that for n>1 is robust.2. We studied the doubly degenerate Habbard model in infinite dimensions by using the dynamical mean field theory, and to obtained ground stats place diagram. We obtained perfectly ferromagnetic ground state for n=1 and n>1 while we did not find ferromagnetic for n<1. We also found phase separation for n<similar or equal>1 and n<less than oFrom above results we established that the Hand's rule coupling which accompanies orbital degeneracy is quite effective in realizing ferromagnetism. Especially the so-called double-exchange mechanism stabilizes metallic ferromagnetism for n>1.3. We constructed a single-site approximation for the single particle Green's function in the double exchange model. By using this Green's function are calculated the magnetic susceptibility and the electrical conductivity.4. We obtained the ground state phase diagram of the double exchange model in infinite dimensions taking into account of full quantum effects of spins.