1. Quantum-Phase Electronics Center and Department of Applied Physics, the University of Tokyo, Tokyo 113-8656, Japan
2. RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
3. Department of Physics, the University of Tokyo, Tokyo 113-0033, Japan
4. The Institute for Solid State Physics, the University of Tokyo, Kashiwa 227-8581, Japan
5. Materials Sciences Research Center, Japan Atomic Energy Agency, Koto City 679-5148, Hyogo, Japan