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