Proximity effects and Andreev reflection in mesoscopic SNS junction with perfect NS interfaces

Low temperature transport measurements on superconducting film - normal metal wire - superconducting film (SNS) junctions fabricated on the basis of 6 nm thick superconducting polycrystalline PtSi films are reported. The structures with the normal metal wires of two different lengths L=1.5 $\mu$m and L=6$\mu$m and the same widths W=0.3$\mu$m are studied. Zero bias resistance dip related to pair current proximity effect is observed for all junctions whereas the subharmonic energy gap structure originating from phase coherent multiple Andreev reflections have occurs only in the SNS junctions with short wires.Comment: ReVTex, 4 pages, 4 eps figures include

Evidence of two-electron tunneling interference in Nb/InAs junctions

The impact of junction transparency in driving phase-coherent charge transfer across diffusive semiconductor-superconductor junctions is demonstrated. We present conductivity data for a set of Nb-InAs junctions differing only in interface transparency. Our experimental findings are analyzed within the quasi-classical Green-function approach and unambiguously show the physical processes giving rise to the observed excess zero-bias conductivity.Comment: 10 pages (RevTex), 4 figures (PostScript), accepted for pubblication in Physical Review

Multiple Andreev Reflection and Giant Excess Noise in Diffusive Superconductor/Normal-Metal/Superconductor Junctions

We have studied superconductor/normal metal/superconductor (SNS) junctions consisting of short Au or Cu wires between Nb or Al banks. The Nb based junctions display inherent electron heating effects induced by the high thermal resistance of the NS boundaries. The Al based junctions show in addition subharmonic gap structures in the differential conductance dI/dV and a pronounced peak in the excess noise at very low voltages V. We suggest that the noise peak is caused by fluctuations of the supercurrent at the onset of Josephson coupling between the superconducting banks. At intermediate temperatures where the supercurrent is suppressed a noise contribution ~1/V remains, which may be interpreted as shot noise originating from large multiple charges.Comment: 7 pages, 7 figures, extended versio