Microwave Response of Superconducting YBa2Cu3O7-delta Nanowire Bridges Sustaining the Critical Depairing Current: Evidence of Josephson-like Behavior

We have investigated the zero-field critical supercurrent of YBa2Cu3O7-? bridges patterned from 50 nm thick films as a function of bridge width, ranging from 2 ?m to 50 nm. The critical current density monotonically increases for decreasing bridge width even for widths smaller than the Pearl length. This behavior is accounted for by considering current crowding effects at the junction between the bridge and the wider electrodes. Comparison to numerical calculations of the current distributions in our bridge geometries of various widths yields a (local) critical current density at 4.2 K of 1.3×108 A/cm2, the Ginzburg Landau depairing current density. The observation of up to 160 Shapiro-like steps in the current voltage characteristics under microwave irradiation substantiates the pristine character of our nanobridges with cross sections as small as 50×50 nm2.