1. Graduate School of Science, University of Hyogo, Kamigori, Hyogo 678-1297, Japan
2. Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan
3. Cryogenic Research Center, The University of Tokyo, Bunkyo, Tokyo 113-0032, Japan
4. Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
5. Institute of Physics, The University of Tokyo, Tokyo 153-8902, Japan