Improved Nanopatterning for YBCO Nanowires Approaching the Depairing Current

An improved nanopatterning procedure has been developed to obtain YBa₂Cu₃O_7-x nanowires with cross-sections as small as 50 × 50 nm², protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 10⁸ A/cm² have been achieved at T = 4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to T_c, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with nanowires without the Au capping layer.