1. Department of Physics, Kyushu University, Fukuoka 812-0395, Japan
2. Department of Physics, Niigata University, Niigata 950-2181, Japan
3. Department of Chemistry, Kyushu University, Fukuoka 812-0395, Japan
4. Department of Materials Process Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan