1. Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
2. College of Liberal Arts and Sciences, Tokyo Medical and Dental University, Ichikawa, Chiba 272-0827, Japan
3. Cryogenic Research Center, The University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
4. Toyota Central R&D Laboratories, Inc., Nagakute, Aichi 480-1192, Japan