A network of nano-twins was seen for the first time in high-energy ion-bombarded samples. This structure was shown to form only at doses above 1011/cm2 and had therefore not been revealed by earlier electron microscopic studies. In this high-dose regime, the familiar columnar defects were linked by the nano-twin structure; thus affecting the bulk superconducting properties.

Nanotwin Networks Connecting Columnar Defects in YBa2Cu3O7-δ and Implications for Magnetic Vortex Interactions. Y.Yan, M.A.Kirk: Philosophical Magazine Letters, 1999, 79[10], 841-8