Combining photoemission and optical spectroscopies for reliable valence determination in YbS and Yb metal
M. Matsunami, A. Chainani, M. Taguchi, R. Eguchi, Y. Ishida, Y. Takata, H. Okamura, T. Nanba, M. Yabashi, K. Tamasaku, Y. Nishino, T. Ishikawa, Y. Senba, H. Ohashi, N. Tsujii, A. Ochiai, S. Shin.