Manifestation of screening effects and A-O covalency in the core level spectra of A site elements in the ABO₃ structure of Ca_1−xSr_xRuO₃

We investigate the evolution of Ca 2p and Sr 3d core level spectra in Ca_1−xSr_xRuO₃ using photoemission spectroscopy. Core level spectra in this system exhibit multiple features and unusual evolution with the composition and temperatures. Analysis of the core level spectra in conjunction with the band structure results indicates final state effects due to different core hole screening channels. Such screening in the photoemission final states can be attributed to the large A-O covalency in these systems. Changes in the core level spectra with temperature and composition suggest significant modification in A-O (A=Ca∕Sr) covalency in Ca-dominated samples, which gradually reduces with the increase in Sr content and becomes insignificant in SrRuO₃. This study thus provides a direct evidence of cation-oxygen covalency and its evolution with temperature, which may be useful in understanding the unusual ground state properties of these materials.