Growth and Very Anisotropic Upper Critical Field of Single-Crystal Bi2Sr2CaCu2Oy

Abstract

Flaky single crystals of a new high-T _c oxide Bi₂Sr₂CaCu₂O _y with dimensions of the order of 1×1×0.1 mm³ 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 -dH _c2/dT for H//c-axis and H⊥c-axis are 0.39 T/K and 7.3 T/K, respectively. The ratio of -dH _c2 ^⊥/dT to -dH _c2 ^///dT 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.