Approaching the theoretical depairing current in YBa2Cu3O7-x nanowires

YBa2Cu3O7-x nanowires, with lateral dimensions smaller that 50 nm have been fabricated by a soft etching procedure preserving an Au capping layer on top of the nanostructure. We have obtained YBCO nanowires carrying critical current densities Jc close to the theoretical depairing limit. The resistive transition and the Jc as a function of temperature of the Au capped nanostructures have been compared with those where the Au protective layer was subsequently removed. We conclude that the Au capping layer together with the soft etching procedure are instrumental in preserving shape pristine superconducting properties very close to the as grown film. Our results open new perspective for the use of YBCO nanostructures in fundamental studies aiming at shedding light on the mechanism for high critical temperature superconductivity.