1. Japan Science and Technology Corporation, NEC Corporation, 34 Miyukigaoka, Tsukuba 305-8501, Japan; Department of Physics, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya 468-8502, Japan; Department of Chemistry, Faculty of Science, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan; Center for Frontier Electronics and Photonics, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan