[1] Hokkaido Univ, Dept Phys, Sapporo, Hokkaido 060, Japan
[2] Aoyama Gakuin Univ, Dept Phys, Setagaya Ku, Tokyo 157, Japan
[3] ISTEC, Superconduct Res Lab, Minato Ku, Tokyo 105, Japan
[4] Univ Tokyo, Dept Superconduct, Bunkyo Ku, Tokyo 113, Japan
[5] Natl Res Inst Met, Ibaraki, Osaka 305, Japan
[6] Ecole Polytech, Solides Irradies Lab, F-91128 Palaiseau, France