Persistent critical current of YBa2Cu3O7-δ nanowires

C-axis oriented YBa2Cu3O7-δ (YBCO) nanowires have been fabricated so as to connect two c-axis oriented semi-ring-shaped YBCO thin films along the c-axis direction. This allows the characterization of high-Tc nanowires with the electrodes being of the same material. Four different lengths of the nanowire arrays were characterized. When the YBCO nanowires were narrower than 100 nm, their persistent critical current revealed an anomalous temperature dependence. The narrow YBCO nanowires behave like superconductor/semiconductor/superconductor junctions with a universal critical current density Jc(T)∝(Tc-T)3/2 at low temperatures. Above a certain temperature T*, the flow of the supercurrent is controlled by thermally activated phase-slip events, with Jc(T) following a power-law dependence Jc∝(Tc-T)α>3/2.