The role of orbital ordering in the formation of electron structure in undoped LaMnO3 manganites in the regime of strong electron correlations

Abstract

The electron structure of undoped LaMnO{sub 3} and slightly doped La{sub 1-x}Sr{sub x}MnO{sub 3} manganites has been calculated within the framework of a generalized tight binding method with explicit allowance for strong intraatomic electron correlations. According to the results of these calculations, the ground state in orbitally disordered undoped LaMnO{sub 3} ferromagnets would be metallic despite the Mott-Hubbard correlation gap in the spectrum of quasiparticles. Owing to the orbital ordering, the insulating state is stabilized in both antiferromagnetic and paramagnetic phases. In-gap states of a polaron nature with a spectral weight proportional to the dopant concentration have been found near the top of the valence band in La{sub 1-x}Sr{sub x}MnO{sub 3}. As the doping level increases, a metal state appears in the ferromagnetic phase, which has a metallic character for one spin subband and an insulating character for the other subband (representing the so-called half-metallic state)