1. Institute for Solid State Physics, University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 106
2. Faculty of General Education, Ehime University, 3, Bunkyo-cho, Matsuyama 790
3. School of Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku-ku, Tokyo 169