Electronic structure of CeRu2X2 (X=Si,Ge) in the paramagnetic phase studied by soft x-ray ARPES and hard x-ray photoelectron spectroscopy

Soft and hard x-ray photoelectron spectroscopy has been performed for one of the heavy fermion system CeRu2Si2 and a 4f-localized ferromagnet CeRu2Ge2 in the paramagnetic phase. The three-dimensional band structures and Fermi surface shapes of CeRu2Si2 have been determined by soft x-ray h nu-dependent angle-resolved photoelectron spectroscopy. The differences in the Fermi surface topology and the non-4f electronic structures between CeRu2Si2 and CeRu2Ge2 are qualitatively explained by the band-structure calculation for both 4f itinerant and localized models, respectively. The Ce valences in CeRu2X2 (X=Si,Ge) at 20 K are quantitatively estimated by the single impurity Anderson model calculation, where the Ce 3d hard x-ray core-level PES and Ce 3d x-ray absorption spectra have shown stronger hybridization and signature for the partial 4f contribution to the conduction electrons in CeRu2Si2.