Evidence for collective pinning in high-temperature superconductors.

Abstract

The relaxation behavior of the remnant moments of two thin-wall rings, one closed and the other open, and powders of various sizes of melt-textured ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ has been investigated. The activation energies (${\mathit{U}}_{0}$'s) obtained are the same at all temperatures in all cases, directly demonstrating that the relaxation in a high-temperature superconductor (HTS) cannot be explained in terms of a distribution of ${\mathit{U}}_{0}$'s associated with different domains as previously suggested. A temperature-dependent pinning volume of flux bundles is necessary to account for the experimental results. A scaling relationship, ${\mathit{U}}_{0}$\ensuremath{\propto}[1-(T/${\mathit{T}}_{\mathit{c}}$${)}^{2}$${]}^{\mathit{m}}$/(${\mathit{BJ}}^{2}$${)}^{\mathit{k}}$, is therefore proposed for such a collective pinning to explain the macroscopic properties of HTS's.