1. Correlated Electron Research Center (CERC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 4, Tsukuba, Ibaraki 305-8562
2. CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012
3. Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656