1. Contribution from the National Institute of Advanced Industrial Science and Technology (AIST), Umezono, 1-1-1, Tsukuba, Ibaraki 305-0012, Japan, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan, and Graduate School of Arts and Sciences, the University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan