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

We report the first contact-free measurements of the upper critical fields, Hc2(T), of single-crystal Y1Ba2Cu3O7-x. In contrast to resistive measurements reported by others, we find that the anisotropy near Tc 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 Hc2 (5), the inferred low-temperature interplanar coherence length (̂>z=7 AÌ̂>) remains larger than the Cu-O layer spacing of 3.9 AÌ̂>. The superconductivity in Y1Ba2Cu3O7-x thus remains fundamentally three dimensional in nature for a substantial temperature range below Tc. © 1987 The American Physical Society.