Electronic structure ofCeRu2X2(X=Si,Ge)in the paramagnetic phase studied by soft x-ray ARPES and hard x-ray photoelectron spectroscopy

Abstract

Soft and hard x-ray photoelectron spectroscopy has been performed for one of the heavy fermion system $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$ and a $4f$-localized ferromagnet $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Ge}}_{2}$ in the paramagnetic phase. The three-dimensional band structures and Fermi surface shapes of $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$ have been determined by soft x-ray $h\ensuremath{\nu}$-dependent angle-resolved photoelectron spectroscopy. The differences in the Fermi surface topology and the non-$4f$ electronic structures between $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$ and $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Ge}}_{2}$ are qualitatively explained by the band-structure calculation for both $4f$ itinerant and localized models, respectively. The Ce valences in $\mathrm{Ce}{\mathrm{Ru}}_{2}{X}_{2}$ $(X=\mathrm{Si},\mathrm{Ge})$ at $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are quantitatively estimated by the single impurity Anderson model calculation, where the $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}3d$ hard x-ray core-level PES and $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}3d$ x-ray absorption spectra have shown stronger hybridization and signature for the partial $4f$ contribution to the conduction electrons in $\mathrm{Ce}{\mathrm{Ru}}_{2}{\mathrm{Si}}_{2}$.