Fig. 1: Resonant inelastic X-ray scattering (RIXS) process in perovskite oxides.

a General lanthanum perovskite oxide structure and scheme of orbital overlap based on radial wave functions. TM represents transition metal ion. b Scheme of the X-ray absorption and RIXS process in La. 3D1 and 3P1 depict the atomic terms of 4d94f1 electronic configuration. Charge transfer between ligands and metal centers is denoted as CT. c High-resolution RIXS spectra and fitted result. The purple- and green-dashed curves represent the 3D1 and 3D2 RIXS final states (electronic configuration 5p54f1), respectively. The error bars are defined by the square root of the cumulative photon counts.