Weak-link-free behaviour of high-angle YBa2Cu3O7–δ grain boundaries in high magnetic fields

Abstract

A CRUCIAL issue in both the physics and the application of high-temperature superconductors is the low transport critical current density (Jct) of polycrystalline materials. Much thinking about this issue has been defined by the thin-film YBa2Cu3O7–δ bicrystal experiments of Dimos et al.1,2, which clearly showed greatly reduced values of Jct at high-angle grain boundaries (mis-orientation angle ≳ 10°). The reproducibility of this result for a wide range of misorientation relationships led them to conclude that all high-angle grain boundaries act intrinsically as Josephson junctions. By contrast, we describe here two high-angle grain boundaries with superconducting properties that clearly lack the weak-link signatures characteristic of Josephson junctions. Our bulk-scale bicrystal results provide direct evidence that not all high-angle grain boundaries are alike in their superconducting properties, and that at least some high-angle boundaries can carry significant supercurrents at 77 K in high magnetic fields.