1. Institute for Materials Research, Tohoku University, Sendai 113-0034, Japan
2. Department of Physics, Niigata University, Niigata 950-2181, Japan
3. KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
4. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
5. Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People's Republic in China
6. Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
7. Graduate School of Science and Engineering, Kagoshima University, Kagoshima 980-0065, Japan