DFT-based resonant inelastic scattering study of LaCoO₃, CoO and LaCoO₃/LaTiO₃ superlattices

Cobalt-based transition metal oxides show a variety of electronic and magnetic behaviors stemming from the multiple electronic configurations Co cations can adopt.  Recently synthesized LaCoO₃/LaTiO₃ superlattices display strong orbital polarization [1]. Density functional theory (DFT) calculations showed that Co cations in LaCoO₃ have the primarily 3+ low-spin state, while Co in the superlattices is 2+ with high-spin. The Co 2+ character is similar to CoO [2,3], but Co-O hybridization is stronger in the superlattice.

Here, we describe Resonant Inelastic X-ray Scattering (RIXS) results on bulk and superlattice materials. The RIXS measurements are modeled using both spin dependent DFT-based theory and canonical atomic multiplet models to understand local electronic states and low energy excitations. We compare the DFT-based RIXS method, which naturally describes electronic bands but greatly simplifies the description of atomic multiplets, to atomic multiplet calculations, which do not contain the band-like features of condensed matter systems. We highlight the attributes of the DFT+U approach; for example, the DFT+U based model is capable of describing the broad fluorescence RIXS features that are characteristically found in nickelates and cobaltates.