Temperature dependence of soft X-ray photoemission spectra for YbCuSi

Yasui, Akira; Fujimori, Shinichi   ; Kawasaki, Ikuto  ; Okane, Tetsuo  ; Takeda, Yukiharu   ; Saito, Yuji  ; Yamagami, Hiroshi; Sekiyama, Akira*; Settai, Rikio*; Matsuda, Tatsuma; Haga, Yoshinori   ; Onuki, Yoshichika*

YbCuSi is a valence fluctuating compounds. Though there are a few temperature-dependent photoemission spectroscopy (PES) measurements, it has been not yet known whether the peak position of the Yb 4 state show the temperature dependence, that relates to the formation of the heavy fermion state. The previous studies were performed by using the vacuum ultraviolet (VUV) radiation. The VUV-PES spectra have considerably large contribution of the surface state. In order to examine the temperature dependence of the bulk electronic state in detail, we have performed the soft X-ray PES (SX-PES) for YbCuSi at BL23SU in SPring-8. With increasing temperatures, the bulk Yb 4 peaks shift toward the higher energy side, while the Yb multiplets do not move. Since the energy shift cannot be explained in the single impurity Anderson model, the experimental results indicate the Kondo lattice effects play important roles for YbCuSi.