Soft Nanostructuring of YBCO Josephson Junctions by Phase Separation

We have developed a new method to fabricate biepitaxial YBa2Cu3O7-delta (YBCO) Josephson junctions at the nanoscale allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures By using the competition between the superconducting YBCO and the insulating Y-2 BaCuO5 phases during film growth we formed nanometer sized grain boundary junctions in the insulating Y2BaCuO5 matrix as confirmed by high resolution transmission electron microscopy Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries