[1] Photodynamics Research Center, Inst. of Phys and Chem. Res. (RIKEN), 519-1399 Aoba, Aramaki, Aoba-ku, Sendai 980-0845, Japan
[2] Department of Physics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
[3] Materials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
[4] Institute of Solid State Physics, University of Tokyo, Kashiwa, Chiba 227-8581, Japan
[5] Institute of Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan