1. Department of Applied Physics, Fukuoka University, Jonan, Fukuoka 814-0180, Japan
2. Department of Electrical Engineering, Tokyo University of Science, Yamaguchi, Sanyo-Onoda, Yamaguchi 756-0884, Japan
3. Asahi Kasei Corporation, Fuji, Shizuoka 416-8501, Japan
4. The Noguchi Institute, Itabashi, Tokyo 173-0003, Japan