1. Department of Applied Physics, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan, School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Nomi City, Ishikawa, 923-1292, Japan, and Department of Mechano-Micro Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan