1. Physics Department, Sapporo Campus, Hokkaido-Kyouiku University, Sapporo 002
2. Institute of Physics, Collge of Arts and Sciences, University of Tokyo, Komaba 153
3. Institute of Material Science, University of Tsukuba, Tsukuba, Ibaraki 305
4. Department of Physics, Faculty of Science, Tohoku University, Sendai 980