Ion beam controllable modification of YBa2Cu3O7−x superconducting thin films

The superconducting transport properties of high-quality epitaxial YBa2Cu3O7−x thin films have been controllably modified using Ar+ ion implantation. It was found that both the critical current density Jc and the superconducting transition temperature Tc significantly decreased with fluence. However, when Jc (at 77 K, H=0) decreased by six orders of magnitude, Tc only decreased from 89 to 77.5 K. A fluence of 5×1012 Ar/cm2 was sufficient to reduce Jc near zero, but Tc still remained above 77 K. We have observed the structure and the morphology of the sample using x-ray diffraction and high-resolution transmission electron microscopy. A film irradiated with Ar+ ions became semiconductor at a bombardment fluence of about 1.2×1013 Ar/cm2, while its superconducting state completely disappeared for an Ar+ dose of about 2.2×1013 Ar/cm2. An Ar+ fluence of 5×1014 Ar/cm2 made the sample amorphous with so high resistivity that it could be treated as insulator. The experimental results showed the possibility of fabricating Josephson junction devices from YBa2Cu3O7−x superconducting thin films and patterning this kind of films by ion implantation technique.