Growth and very anisotropic upper critical field of single-crystal bi₂sr₂cacu₂o_y

Flaky single crystals of a new high-T_coxide Bi₂Sr₂CaCu₂O_ywith dimensions of the order of 1×1×0.1 mm³have been prepared using a CuO flux method. The electrical resistivity shows a sharp superconducting transition at 80.6 K. The upper critical field H_c2was determined to be very anisotropic. The values of -dH_c2dT 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_c2dT 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.