Ion beam controllable modification of YBa2Cu3O7 - x superconducting thin films

The superconducting transport properties of high-quality epitaxial YBa₂Cu₃O_7-x thin films have been controllably modified using Ar⁺ ion implantation. It was found that both the critical current density J_c and the superconducting transition temperature T_c significantly decreased with fluence. However, when J_c (at 77 K, H=0) decreased by six orders of magnitude, T_c only decreased from 89 to 77.5 K. A fluence of 5×10¹² Ar/cm² was sufficient to reduce J_c near zero, but T_c 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 YBa₂Cu₃O_7-x superconducting thin films and patterning this kind of films by ion implantation technique.