1. Department of Physics, Keio University, Yokohama 223-8552, Japan
2. The Center for Emergent Matter Science, RIKEN, Wako, Saitama 351-0198, Japan
3. Center for Liberal Arts and Sciences, Ashikaga University, Ashikaga, Tochigi 326-8558, Japan
4. Cryogenic Research Center, University of Tokyo, Bunkyo, Tokyo 113-0032, Japan