Anisotropic upper critical fields of highly oriented Bi-Sr-Ca-Cu-O thin films prepared by coevaporation

Two kinds of thin films with a zero resistance T c of 82 K and 103 K, respectively were prepared on an MgO substrate by coevaporation in the Bi-Sr-Ca-Cu-O system. Both films have a strong preferred orientation with the c -axis perpendicular to the film plane. The upper critical field H c2 was measured for these two films. The anisotropy, that is, the ratio of -d H c2 ⊥ /d T to -d H c2 // /d T is about 20 for both the 85 K phase and 110 K phase and is larger than that of YBa 2 Cu 3 O x . The estimation of the values of H c2 ⊥ (0) results in about 440 T for the 85 K phase and about 500 T for the 110 K phase.