1. Department of Physics, Graduate School of Science, Tohoku University, 6‐3 Aoba, Aramaki, Aoba‐ku, Sendai, Miyagi, 980‐8578, Japan, http://sspns.phys.tohoku.ac.jp/index.html
2. WPI ‐ Advanced Institute for Materials Research (WPI‐AIMR), Tohoku University, 2‐1‐1 Katahira, Aoba‐ku, Sendai, Miyagi, 980‐8577, Japan, http://www.wpi‐aimr.tohoku.ac.jp/jp/index.html