1. Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
2. Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
3. Toyota Central Research & Development Laboratories, Inc., Nagakute, Aichi 480-1192, Japan
4. Department of Physics & Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
5. Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
6. Department of Applied Physics, KTH Royal Institute of Technology, Electrum 229, SE-16440 Stockholm Kista, Sweden
7. Research Center for Low Temperature and Material Sciences, Kyoto University, Kyoto 606-8501, Japan