Anisotropic nature of high-temperature superconductivity in single-crystal Y1Ba2Cu3O7−x

Abstract

We report the first contact-free measurements of the upper critical fields, ${\mathrm{H}}_{\mathrm{c}2}$(T), of single-crystal ${\mathrm{Y}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. In contrast to resistive measurements reported by others, we find that the anisotropy near ${\mathrm{T}}_{\mathrm{c}}$ is temperature independent in agreement with the expectations of anisotropic Ginzburg-Landau theory. Estimates of the anisotropic Ginzburg-Landau and London parameters are reported. These indicate that despite the large anisotropy in ${\mathrm{H}}_{\mathrm{c}2}$ (5:1), the inferred low-temperature interplanar coherence length (${\xi }_{\mathrm{z}}$=7 Å) remains larger than the Cu-O layer spacing of 3.9 Å. The superconductivity in ${\mathrm{Y}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ thus remains fundamentally three dimensional in nature for a substantial temperature range below ${\mathrm{T}}_{\mathrm{c}}$.