1. RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
2. Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Hongo, Tokyo 113-8656, Japan
3. Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
4. Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan