1. Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo 113-8656, Japan
2. Department of Advanced Materials Science, The University of Tokyo, Kashiwa 277-8561, Japan
3. Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany
4. RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
5. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
6. PRESTO, Japan Science and Technology Agency (JST), Tokyo 102-0075, Japan