Diffusive single and multiply connected SNS systems with high-transparent interfaces

We present low-temperature transport measurements on single and multiply connected SNS systems fabricated on the basis of superconducting polycrystalline PtSi film. Zero bias anomaly (ZBA) and subharmonic energy gap structure (SGS) originating from the proximity effects and the multiple Andreev reflections were observed and carefully studied. It was found that the ZBA is not described by any theories developed for SNS junctions with high-transparent NS interface. The value of excess conductance and the width of ZBA for single SNS junction far exceed values predicted by up-to-date theories.
The NS interfaces of our SNS junctions are really hightransparent, for superconducting and normal metal parts are made of the same material. On the other hand, as we have to deal with long diffusive SNS junctions one might expect that impurities could provide the conditions for incoherent multiple Andreev reflections.
In comparison with single SNS junctions we observe significant narrowing of the ZBA in multiply connected SNS systems: one-dimensional ($\mathrm{1D}$) and two-dimensional arrays ($\mathrm{2D}$) of SNS junctions. In $\mathrm{2D}$ arrays an appreciable SGS appears, with up to $n=16$ ($eV=\pm2\Delta/n$) and some numbers being lost. One of the most interesting results obtained on $\mathrm{1D}$ arrays consists in the appearance of symmetrical dips on the dependences $\mathrm{d}V/\mathrm{d}I-V$ at dc voltage corresponding to some multiples of $\Delta/e$. Presented results show that coherent phenomena governed by Andreev reflection are not self-averaging and are maintained over a macroscopic scale.