Large Anisotropy of the Upper Critical Magnetic Field in Single Crystal Bi-(Sr, Ca)-Cu-O

Abstract

Single crystals of a recently discovered high-T _c Bi-(Sr, Ca)-Cu-O compound have been obtained. EPMA analysis exhibited that the compositional ratio of the crystal is 2-3-2. X-ray diffraction and transmission electron diffraction analysis revealed that the crystal has a layered structure characterized by orthorhombic symmetry with the lattice constant a=5.405 Å, b=5a and c=30.69 Å. The upper critical magnetic field H _c2 has been measured for the superconducting single crystal. The anisotropy between the c-axis and the basal plane is much larger than that of Ba₂YCu₃O_7-y or (La_1-x Sr _x )₂CuO_4-y . The slope of temperature dependence of H _c2 along the c-axis is -0.32 T/K, while that along the basal plane is -14±3 T/K. The coherence length along the c-axis is estimated to be 1.0±0.1 Å, and that in the basal plane is 42 Å. The anisotropy factor is 44±9. These values suggest that the two-dimensionality in electronic structure for this superconductor is much stronger than other high-T _c oxides.