Surface, final state, and spin effects in the valence-band photoemission spectra of LaCoO3 (001)

The electronic structure of a LaCoO3(001) perovskite is analyzed using simulated and measured angle-resolved valence-band photoemission spectroscopy data with emphasis on the effects of the surface truncation, the final state effects, and the spin degeneracy removal. Supercell simulations reveal instability towards the formation of nonuniform spin polarization in the Co-containing layers under tensile stress. Lattice expansion reduces antiferrodistortive octahedron tilting and tips the ratio between the crystal field parameter and the exchange energy in favor of local magnetization. While the magnitude of the local moment scales with lateral strain, the Curie temperature saturates for straight Co-O-Co chains below 75 K. The comparison of simulated photoemission spectra with experiments suggests Co-O2 to be the most stable surface stoichiometry, as proposed from transport and catalytic studies.