Transport properties of high-Tc planar Josephson junctions fabricated by nanolithography and ion implantation

We have developed a process for fabrication of planar high-Tc Josephson junctions using nanolithography and a 200 keV ion implanter. Conduction occurs in the ab plane and has no metallurgical interface. Devices may be tuned to operate at temperatures between 1 K and the Tc of the undamaged superconducting material by varying the length of the weak link or by changing the amount of ion damage. We have examined the normal state and superconducting properties of these films and find behavior consistent with a de Gennes dirty limit proximity effect model. Current–voltage curves, Ic(T) and R(T) data suggest a temperature dependent superconducting-normal metal interface that we have incorporated into the proximity effect model.