1. Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara 228-8555, Japan, Department of Materials, Faculty of Engineering, Mie University, Tsu, Mie 514, Japan, and Department of Chemistry, Faculty of Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan