The Anti-proximity Effect and More: Novel Phenomena in 1D Superconductors
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the important role played by thermal and quantum fluctuations of the order parameter. This makes the study of quasi 1d nanowires (diameter < superconducting coherence length) a key area for the exploration of novel physics. Experiments on superconducting zinc nanowires with bulk superconducting electrodes showed a counterintuitive phenomenon in which the bulk superconductors destroyed or weakened the superconductivity of the nanowires.
This phenomenon was named the ‘anti-proximity effect’ (APE). Recent experiments on aluminium nanowires (AlNW) appear to bring a complete understanding of the phenomenon and resolve a number of puzzles in the early experiments. In addition measurements of a single resistance reading found switching from the superconducting to the normal state close to Tc of the wire and at low temperatures in the APE regime. The switching at low temperature is triggered by individual quantum phase slips. These results indicate that the low temperature APE regime offers a clean platform for the observation of individual quantum phase slips, a goal eluded in numerous experiments. In ferromagnetic nanowires contacted with superconducting electrodes, a very long range proximity effect, contrary to conventional wisdom is found. It is possible that the effect is related to triplet superconductivity mediated by inhomogeneity at the superconductor-ferromagnet interface.