1. Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510
2. 2-13-7 Tamagawagakuen, Machida, Tokyo 194-0041
3. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581
4. Department of Materials and Technology, Faculty of Engineering, Niigata University, Niigata 950-2181
5. Graduate School of Science, Tohoku University, Sendai 980-8578