1. RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
2. Research and Development Group, Hitachi, Ltd., Hatoyama 350-0395, Japan
3. Department
of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
4. Department of Basic Science, University of Tokyo, Tokyo 153-8902, Japan
5. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan