Spin-disorder-scattering-induced spectral-weight transfer and pseudogap in doped perovskiteLaMnO3

Abstract

The electronic structures of ferromagnetic and paramagnetic states of La${}_{1\ensuremath{-}x}{A}_{x}$MnO${}_{3}$ $(A$=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-${e}_{g}$ 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.