High critical field anisotropy of superconducting Bi-Sr-Ca-Cu oxide from highly oriented thin films

Abstract

Superconducting films of Bi-Sr-Ca-Cu oxides have been grown on MgO substrates by multitarget magnetron sputtering. After post-annealing in an oxygen atmosphere, zero resistance was obtained at about 80 K. X-ray diffraction indicates a high degree of preferential growth of the c axis perpendicular to the substrate. Measurements of the upper critical field Bc2(T) of these films show critical field slopes (B′c2≡−dBc2/dT at Tc) of 8.5 and 0.56 T/K, respectively, for B parallel and perpendicular to the substrate. The anisotropy of ∼15 and the Bc2∥ are the highest values yet reported for high-temperature superconductors.