Spin-disorder-scattering-induced spectral-weight transfer and pseudogap in doped perovskite LaMnO3

The electronic structures of ferromagnetic and paramagnetic states of La1-xAxMnO3 (A=Ca,Sr) have been studied for the doping concentration x=1/3, where the maximum giant magnetoresistance (GMR) occurs. We use the unrestricted Hartree-Fock approximation to treat the correlation effect of the multiband Hubbard model and the real-space recursion method to calculate the density of states. The random spins of the paramagnetic state are taken care of by the usual coherent-potential approximation. In agreement with experiments, our study shows that the ferromagnetic ground state has a very flat Mn-eg band with low density of states at the Fermi energy, while in the paramagnetic state the magnetic scattering narrows the band width and causes a spectral-weight transfer from O-2p to Mn-3d orbitals. In particular, the lower Mn-d Hubbard band is almost fully filled which leads to a pseudogap at the Fermi energy. Our results offer a direct connection between the calculated electronic structure and the experimentally observed resistance increase and metal-insulator transition near the Curie temperature. copyright 1997 The American Physical Society