YBa2Cu3O7-δ Josephson junctions fabricated by oxygen implantation

We report Josephson junctions in YBa2Cu3O7-δ thin films, fabricated by oxygen irradiation at 200 keV through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500 deg. C in an oxygen atmosphere, the implanted region has a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of <15 K. Close to the coupling temperature the critical current shows a nearly complete modulation in an applied magnetic field. This indicates a homogeneous current distribution in the junction. Over the entire temperature range of Josephson coupling, the junctions exhibit resistively shunted junction like I-V characteristics with additional excess current. Furthermore, the exponential dependence of the critical current on temperature is in good agreement with conventional superconductor-normal-superconductor proximity effect theory