Kitayama, S.; Schäfers, F.; Gorgoi, M.; Fujiwara, H.; Gloskovsky, A.; Felser, C.; Funabashi, G.; Yamaguchi, J.; Kimura, M.; Kuwahara, G.; Imada, S.; Higashiya, A.; Tamasaku, K.; Yabashi, M.; Ishikawa, T.; Onuki, Y.; Ebihara, T.; Suga, S.; Sekiyama, A.: Photon Energy dependent Hard X-Ray Photoemission Spectroscopy of YbCu2Si2. Journal of the Physical Society of Japan 81 (2012), p. SB055/1-4

We have performed photon energy (hν) dependent hard X-ray photoemission spectroscopy (HAX- PES) for YbCu2Si2, which is a heavy Fermion compound with intermediate Yb valence. We iden- tified that the bulk components in the Si 1s and Yb 3d spectra develop with increasing hν from 2.5 keV to 6 keV. Moreover, the temperature dependence of the Yb 3 d spectra measured at hν=8 keV has shown a valence fluctuation behavior. These results suggest that high hν HAXPES is essential to determine the mean valence of the Yb compounds.