1. Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan, Department of Electronic Engineering, Tohoku University, 6-6-05, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan, National Institute of Advanced Industrial Science and Technology, 2217-14 Hayashi-cho Takamatsu Kagawa 761-0395, Japan, and Institute for Genome Research, University of Tokushima, 3 Kuramoto-cho, Tokushima, 770-8503, Japan