Hydrogen-induced change in the 4f localization in CeRu2 studied with x-ray photoemission spectroscopy.

Our x-ray photoemission spectroscopy study of ${\mathrm{CeRu}}_{2}$${\mathrm{H}}_{\mathrm{\ensuremath{\approxeq}}4}$ shows the disappearance of a Ce 3d satellite peak which is generally at- tributed to an ${f}^{0}$ final state and a reduction of the ${f}^{2}$-final-state-related intensity. An interpretation in terms of an Anderson model leads to an increase in the f count ${n}_{f}$ from \ensuremath{\approxeq}0.8 to nearly unity and to a change in the 4f\char21{}conduction-band hybridization energy \ensuremath{\Delta} from 120 meV to 60\ifmmode\pm\else\textpm\fi{}20 meV. The observed binding-energy shifts of 0.7 eV (Ce 3d, 5p) and 0.4 eV (Ru 3d) are partly due to the lattice expansion as the 4f bonding contribution disappears. The valence-band spectrum shows weak hydrogen-induced emission at 5\char21{}8 eV. The observation of peaks at \ensuremath{\approxeq}1 eV and \ensuremath{\approxeq}2.6 eV in ${\mathrm{CeRu}}_{2}$ and ${\mathrm{CeRu}}_{2}$${\mathrm{H}}_{\mathrm{\ensuremath{\approxeq}}4}$, respectively, fits well into the ${f}^{1}$-${f}^{0}$ screening scheme.