1. Correlated Electron Research
Group (CERG), RIKEN-Advanced Science Institute, Wako, Saitama 351-0198, Japan
2. Photon Factory and Condensed
Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
3. PRESTO, Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo 102-0075,
Japan