Boundary effect on superconductivity in long single-crystal superconducting nanowires

We fabricate single-crystal Pb, Sn, and Zn nanowires, of length 6 or 60 μm and diameter 30–250 nm, using an in situ template-based electrochemical method. In this approach, a single nanowire is formed in contact with a pair of bulk film electrodes of Au, Sn, or Pb. We observe that, with superconducting electrodes having a higher critical temperature Tc, superconductivity is induced in Sn and Zn nanowires at the Tc of the electrodes for nanowires as long as 60 μm. With Au electrodes, superconductivity is suppressed completely in 6 μm-long nanowires and partially in 60 μm-long nanowires. Based on transmission electron microscopy studies, the nanowires are single crystalline. Analysis of the temperature dependence of the normalized resistance suggests that the residual-resistance-ratio plays an important role in the observed anomalous long-range proximity effect.