Crystalline electric field effects in Ce3d core-level spectra of heavy-fermion systems: Hard x-ray photoemission spectroscopy on CeNi1-x Cox Ge2

High-resolution hard x-ray photoemission measurements have been performed to clarify the electronic structure originating from the strong correlation between electrons in bulk Ce3d core-level spectra of CeNi1-x Cox Ge2 (0≤x≤1). In the Ce3 d5/2 core-level spectra, the variation in satellite structures (f2 peaks) shows that the hybridization strength between Ce4f and conduction electrons gradually increases with Co concentration in good agreement with the results of Ce3d-4f and 4d-4f -resonant photoemission spectroscopies. Particularly, in Ce3 d3/2 core-level spectra the multiplet structures of f1 peaks systematically change with the degeneracy of f states which originates from crystalline electric field effects.