1. Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397
2. Department of Physics, Tokyo Institute of Technology, Oh-okayama, Tokyo 152-8551
3. Department of Physics, Tohoku University, Sendai 980-8578
4. Department of Material Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561
5. The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047