1. Physics Department, Graduate School of Science, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai 980-8578
2. National Institute for Materials Science, Tsukuba 305-0047
3. Institute of Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577
4. Center for Low Temperature Science, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai 980-8578