1. Department of Physics, Faculty of Science and Engineering, Chuo University, Bunkyo, Tokyo 112-8551, Japan
2. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
3. Quantum Matter Program, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashihiroshima, Hiroshima 739-8530, Japan