1. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
2. Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195
3. Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
4. Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522
5. Department of Materials Science and Engineering, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.
6. Department of Physics, Faculty of Science, Kobe University, Kobe 657-8501