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[en] In normalmetal/superconductor hybrid structures nonlocal conductance is determined by crossed Andreev reflection (CAR) and elastic cotunneling (EC). This was investigated recently both experimentally and theoretically. Dynamical Coulomb blockade of EC and CAR was predicted theoretically. Here we report on experimental investigations of these effects. We found signatures of dynamical Coulomb blockade in local and nonlocal conductance in the normal state. In the superconducting state, we find s-shaped nonlocal differential conductance curves as a function of bias applied on both contacts. These curves were observed for bias voltages both below and above the gap. We compare our results to theory.
[en] A phenomenological investigation of the dc Josephson current in superconductor endash (S-) normal-metal endash (N) [semiconductor endash (Sm-)] superconductor junctions is carried out as a function of the carrier concentration in the barrier. The occurrence of a nonmonotonic dependence of the Josephson current on the carrier concentration is predicted within some limits. This study suggests that in S-N- (Sm-) S structures there is an optimum carrier concentration range which gives the maximum value of the Josephson current IC and the junction parameter ICRN. copyright 1997 The American Physical Society
[en] A study was made of variable-thickness superconducting bridges made of tin and indium. The current-voltage characteristics were determined for these bridges as a function of their length and width. The characteristics exhibited a linear region as well as an inflection. The temperature of the appearance of such an inflection depended on the length of the bridge but was independent of the bridge material
[en] The use of suspended stencils in the self aligned fabrication of niobium lead tunnel junctions has been investigated. It is shown that while all-polymer masks are unsatisfactory for this application, suspended aluminum stencils supported on polyimide can be used to make these junctions with good current-voltage characteristics. This stencil, which can be baked to at least 2000C, is made using e-beam lithography, lift off and plasma etching in oxygen. With this technique, junctions with submicron dimensions have been fabricated in a single masking step without any surface cleaning of the niobium film. The current-voltage characteristic of these junctions do not show the knee structure which is generally attributed to a contamination or damaged layer on the niobium surface
[en] We calculate the ac and dc current-voltage (I-V) relation when a tunnel barrier is placed in the normal region of a superconductor endash normal-metal endash superconductor (S1NS2) junction, where the two superconducting contacts have different gaps (Δ2≥Δ1≥0). The voltages at which subharmonic gap structure (SGS) appears in the zero-temperature I-V are the same as previously found for the SGS in ballistic S1NS2 junctions at a finite temperature. Some of the SGS close-quote s are strong enough to produce negative differential resistance. We determine the variation of the ac Josephson current with bias, junction transmissivity, gap ratio Δ1/Δ2, and junction length L. The ac Josephson current through a ballistic SNS junction can also be used to measure the superconducting phase difference φ. copyright 1997 The American Physical Society