Microstructure and superconductivity of Zn and Au-Sn junction nanowires

In this report, we investigated the fabrication, structural characterization, and transport properties of Zn and Au-Sn junction nanowires with diameters ranging from 40 to 100 nm. Both nanowires were fabricated by electro-depositing metals into commercially available polycarbonate (PC) or anodic aluminum oxide (AAO) membranes. Zn nanowire could be single-crystal or polycrystalline by controlling the electro-deposition process. Transport studies have shown that the superconducting transition temperature Tc is insensitive to the nanowire diameter and morphology. The superconductivity shows a clear crossover from bulk-like to quasi-1d behavior when the diameter of the wires is reduced to 70 nm (20 times smaller than the bulk coherence length). The Au/Sn junction nanowires, which consist of two intermetallic phases, AuSn and AuSn4, have shown three superconducting transitions corresponding to pure Sn, AuSn, and AuSn4. Mechanisms for the formation of these intermetallic phases and the effect of these phases on the superconductivity of striped nanowires are also discussed.