1. Department of Physics, Keio University, Yokohama 223-8522, Japan
2. Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8521, Japan
3. Department of Physics, Ehime University, Matsuyama 790-8577, Japan
4. Department of Chemistry, Kyushu University, Fukuoka 819-0395, Japan