1. The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581
2. Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501
3. Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501
4. Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297