1. Institute of Materials Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305
2. National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305
3. Superconductivity Research Laboratory, Nagoya Division, International Superconductivity Technology Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456