1. Department of Applied Physics and Quantum Phase Electronics CenterUniversity of Tokyo Tokyo 113‐8656 Japan
2. RIKEN Center for Emergent Matter Science (CEMS) Wako 351‐0198 Japan
3. PRESTOJapan Science and Technology Agency (JST) Chiyoda‐ku Tokyo 102‐0075 Japan
4. Institute for Solid State PhysicsUniversity of Tokyo Kashiwanoha Kashiwa 277‐8581 Japan