1. Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
2. PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan
3. R&D Laboratory, Stanley Electric Co., 1-3-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa 225-0014, Japan