Thomas Kimber Worthington

The anisotropic nature of the superconducting properties of single crystal Y1Ba2Cu3O7 − x

Abstract A series of noncontact magnetic measurements on high-quality single crystals of Y1Ba2Cu3O7 − x have enabled us to demonstrate that the superconducting-state properties of Y1Ba2Cu3O7 − x are those of a conventional, anisotropic superconductor with the anisotropy being associated with the highly conducting Cu O sheets in the Y1Ba2Cu3O7 − x crystal structure. The anisotropy in the superconducting state is reflected most strongly in the critical current anisotropy, which is as large as 20 to 1 at low temperatures and low fields and gets arbitrarily large at higher temperatures and higher fields. The upper critical field HC2 shows an anisotropy that varies from 6:1 to 10:1 in different crystals of high quality. Along the copper-oxygen sheets the upper critical field is enormous, extrapolating to ∼60 Tesla by 77 K and implying a low-temperature Ginzburg-Landau coherence length normal to the layers of 2A− 4A. Strong upward curvature is evident in the HC2 data in both orientations of applied field. This curvature can be interpreted in terms of thermodynamic fluctuations, and, if this explanation is correct, the critical region is enormous, extending more than 25 K below TC.

Crystal growth and characterization of the superconducting phase in the BiSrCuO system

Crystal growth was investigated in the system BiSrCuO. Layered bismuth cuprates with formulas close to (Bi, Sr)4CuOx or (Bi, Sr)5Cu2Ox and a typical micaceous, lath-like habit were grown by slow cooling from a wide range of compositions partially or totally melted in the temperature range 890–1000°C. Only (Bi, Sr)4CuOx crystals with 0.8<Sr/Bi<0.9 were superconducting, with Tc9–10 K. In Sr-rich melts, platy crystals of orthorhombic SrCuO2 and SrCu1.7Ox were obtained. BiSrCuO melts react with platinum below ca. 1000°C, leading to the formation of Sr4PtO6 crystals.

Manifestation of “staircase vortices” in angular dependence of the irreversible boundary of YBaCuO crystals

Abstract We report an observation of a double peak in the lossy component of complex susceptibility χ″ in single crystals of YBaCuO. This double peak appears over a finite range of applied dc magnetic fields and intermediated field orientations. We attribute this phenomenon to two components of J c , which arise from a “staircase vortex” pattern, where portions of the vortex lie between CuO layers.

Anisotropy in Single-Crystal Y 1 Ba 2 Cu 3 O 7−x

Considerable activity on high-Tc superconductivity in Cu-O based perovskites has followed the breakthrough discovery of superconductivity in this class of materials by Bednorz and Muller1. Nevertheless, the macroscopic nature of the superconductivity in these new materials and the mechanism responsible for their superconductivity are still unclear. The recent availability of single crystals of the new Cu-O based superconductors has led to the observation of considerable anisotropy in resistivity2, critical current density3, and upper2,4–7 and lower3 critical fields. In this paper we summarize our recent measurements of Hc2, Hc1, and critical current density as a function of orientation for single crystal Y1Ba2Cu3O7−x. We use this data to estimate the anisotropic Ginzburg-Landau parameters. We find that the anisotropic Ginzburg-Landau theory describes our data well near Tc and that, although the superconductivity in Y1Ba2Cu3O7−x is strongly anisotropic, it is three dimensional in nature. Elaborations of available theories are needed to explain lower temperature features of our data.