SPIN-DISORDER-SCATTERING-INDUCED SPECTRAL-WEIGHT TRANSFER AND PSEUDOGAP IN DOPED PEROVSKITE LAMNO3

The electronic structures of ferromagnetic and paramagnetic states of La(1-x)A(x)MnO(3) (A=Ca,Sr) have been studied for the doping concentra tion x=1/3, when the maximum giant magnetoresistance (GMR) occurs. We use the unrestricted Hartree-Fock approximation to treat the correlati on effect of the multiband Hubbard model and the real-space recursion method to calculate the density of states. The random spins of the par amagnetic state are taken care of by the usual coherent-potential appr oximation. In agreement with experiments, our study shows that the fer romagnetic ground state has a very flat Mn-e(g) band with low density of states at the Fermi energy, while in the paramagnetic state the mag netic scattering narrows the band width and causes a spectral weight t ransfer from O-2p to Mn-3d orbitals. In particular, the lower Mn-d Hub bard band is almost fully filled which leads to a pseudogap at the Fer mi energy. Our results offer a direct connection between the calculate d electronic structure and the experimentally observed resistance incr ease and metal-insulator transition near the Curie temperature.