  We investigate the evolution of Ca 2p and Sr 3d core level spectra in
Ca(1-x)SrxRuO3 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 reveal novel final state effects due to different core hole
screening channels. Changes in the core level spectra suggest significant
modification in Ca-O covalency in Ca dominated samples, which gradually reduces
with the increase in Sr content and becomes minimum in SrRuO3. This study thus,
provides a direct evidence of the role of cation-oxygen covalency in the ground
state properties of these novel materials.
