Low-energy orbital excitations in strained LaCoO3 films

We present 90 meV resolved Co 2 p 3 d resonant inelastic x-ray scattering linear dichroism spectra of strained LaCoO 3 films and a LaCoO 3 single crystal. A polarization-dependent low-energy excitation is observed at ∼ 0.2 eV on the tensile-strained LaCoO 3 / SrTiO 3 film, while it is not observed in either bulk LaCoO 3 or the compressive-strained LaCoO 3 / LaAlO 3 film. Guided by cluster calculations, we are able to distinguish the spin-state manifolds close to their transition point of Co 3 + ions in LaCoO 3 systems. Through a polarization analysis, we show that the spin state can easily flip from a low-spin 1 A 1 g state in an octahedral symmetry to the high-spin 5 B 2 g or 5 E g states with a small tetragonal distortion. A mixture of spin states suggests that the high-spin Co 3 + plays an important role in long-range ferromagnetic order on both tensile- and compressive-strained LaCoO 3 films.