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