Ion-beam modification of cuprate superconductors on a sub-μm scale

Full text: Ion irradiation together with appropriate masking techniques and state-of-the-art ion optics bears the potential to create nanostructures in thin films of cuprate superconductors. We present investigations on thin YBa2Cu3O7 films after cumulative irradiation with He+ ions. Some of the films were grown epitaxially on MgO substrates with the CuO2 planes oriented parallel to the substrate surface. Measurements of the x-ray diffraction, electrical resistivity and the Hall effect consistently indicate an increase of point defects. These defects result in a systematic decrease of the critical temperature, increase of resistivity and, finally, in a transition to a semiconducting or even insulating state. A significant dependence of the defect concentration on the angle of incidence of the ion beam relative to the surface of the thin HTS films was predicted by computer simulation of the ion-target interactions with the program code MARLOWE that is based on an evaluation of the entire collision cascades and the exact crystalline structure of the target material. Measurements of the electrical resistivity after ion irradiation at different angles confirm this behaviour. YBa2Cu3O7 thin films grown on vicinal SrTiO3 substrates allow for a simultaneous determination of in-plane and out-of-plane resistivity. In unirradiated YBa2Cu3O7 the resistivity exhibits a metallic behaviour in all crystallographic directions. Irradiation at a dose of about 1015 cm-2 changes the out-of-plane resistivity to a thermally-activated behaviour, whereas the in-plane resistivity remains metallic, and increases the electrical anisotropy. (author)