'Nanotwin' networks connecting columnar defects in YBa2Cu3O7-delta and implications for magnetic vortex interactions

A unique structure, a network of nanotwins, is revealed for the first time in high-energy ion-irradiated YBa₂Cu₃O_7-delta. This structure is shown to form only at ion doses of 1011 cm-2 or greater and thus is not revealed in any earlier electron microscopy studies. In this higher-dose regime, the well known columnar defects are connected by the nanotwin structure, thus affecting bulk superconducting properties. Consequences for a number of published interpretations of such measurements related to pinning and dynamics of magnetic vortices are discussed.