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 one of valence fluctuating compounds. Though there are a few temperature ()-dependent photoemission spectroscopy (PES) measurements for YbCuSi, there are different interpretations of the obtained spectra with each other. 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 bulk electronic state in detail, it is needed to suppress the surface contribution. The soft X-ray PES (SX-PES) is a powerful tool to investigate the bulk electronic state. The SX-PES measurements were performed at BL23SU in SPring-8. In our SX-PES spectra, the surface Yb 4 contribution is very small. With increasing , 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.