Growth and Very Anisotropic Upper Critical Field of Single-Crystal Bi₂Sr₂CaCu₂O_y

Abstract

Flaky single crystals of a new high- T c oxide Bi 2 Sr 2 CaCu 2 O y with dimensions of the order of 1×1×0.1 mm 3 have been prepared using a CuO flux method. The electrical resistivity shows a sharp superconducting transition at 80.6 K. The upper critical field H c2 was determined to be very anisotropic. The values of -d H c2 /d T for H // c -axis and H ⊥ c -axis are 0.39 T/K and 7.3 T/K, respectively. The ratio of -d H c2 ⊥ /d T to -d H c2 // /d T is 19. The value of H c2 ⊥ (0) for H ⊥ c -axis is estimated to be as large as 400 T. The Ginzburg-Landau coherence length along the c -axis at 0 K ξ // (0) is 2.1 Å, suggesting quasi-two-dimensional superconductivity.