Diffusive single and multiply connectedSNS systems with high-transparentinterfaces

Abstract

We present low-temperature transport measurementson single and multiply connected SNS systems fabricated on thebasis of superconducting polycrystalline PtSi film. Zero biasanomaly (ZBA) and subharmonic energy gap structure (SGS)originating from the proximity effects and the multiple Andreevreflections were observed and carefully studied. It was foundthat the ZBA is not described by any theories developed forSNS junctions with high-transparent NS interface. The value ofexcess conductance and the width of ZBA for single SNSjunction far exceed values predicted by up-to-date theories.The NS interfaces of our SNS junctions are really high-transparent, for superconducting and normal metal parts aremade of the same material. On the other hand, as we have todeal with long diffusive SNS junctions one might expect thatimpurities could provide the conditions for incoherent multipleAndreev reflections.In comparison with single SNS junctions we observe significant narrowing of the ZBA in multiply connected SNS systems:one-dimensional (1D) and two-dimensional arrays (2D) of SNSjunctions. In 2D arrays an appreciable SGS appears, with up to n = 16(eV = ±2Δ/n) and some numbers being lost. One of themost interesting results obtained on 1D arrays consists in theappearance of symmetrical dips on the dependences dV/dI - Vat dc voltage corresponding to some multiples of Δ/e. Presentedresults show that coherent phenomena governed by Andreevreflection are not self-averaging and are maintained over amacroscopic scale.