We report Co L3-edge resonant inelastic X-ray scattering on LaCoO3 at 20 K. We observe excitations with sizable dispersion that we identify as intermediate-spin (IS) states. Theoretical calculations that treat the IS states as mobile excitons propagating on the low-spin (LS) background support the interpretation. The present result shows that mobility substantially reduces the energy of IS excitations in part of the Brillouin zone, which makes them important players in the low-energy physics of LaCoO3 together with immobile high-spin (HS) excitations. * These two authors contributed equally to this work.
We present 90 meV resolved Co 2p3d 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 1g state in an octahedral symmetry to the high-spin 5 B 2g 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.
Angle-dependent 2p3d resonant inelastic X-ray scattering spectra of a LaCoO3 single crystal and a 55 nm LaCoO3 film on a SrTiO3 substrate are presented. Theoretical calculation shows that, with ∼20 meV resolved Co 2p3d resonant inelastic X-ray scattering (RIXS), the excited states of the isotropic 1A1g(Oh) ground state are split by 3d spin–orbit coupling, which can be distinguished via their angular dependence. However, strong self-absorption and saturation effects distort the spectra of the LaCoO3 single crystal and limit the observation of small angular dependence. In contrast, the RIXS on 55 nm LaCoO3 shows less self-absorption effects and preserves the angular dependence of the excited states.
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