a Energy diagrams for low-Tc and high-Tc nanowires. Energies below and above 2Δ are shown in blue and red, respectively. b Scanning electron micrograph of an YBCO nanowire shaped by two FIB cuts across a microbridge. The YBCO film, STO substrate and FIB cuts are shown in gray, blue, and black, respectively. The scale bar corresponds to 5 μm. c IV curve of a 55-nm-wide YBCO nanowire at 4.2 K. Inset: temperature dependences of the average switching Is (orange circles) and retrapping Ir (blue squares) currents. Source data are provided as a Source Data file.