1. The Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581
2. CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012
3. The Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Osaka 567-0047
4. Research Institute for Computational Sciences (RICS), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568
5. Nano Electronics Research Laboratories, NEC Corporation, Tsukuba, Ibaraki 305-8501