Influence of magnetic field and Pincus states in normal-metal-superconductor tunnel junctions.

摘要: Normal-metal---superconductor tunneling, when applied to metallic superconductors with well-known bulk properties, yields useful information on barrier properties. In particular, it is quite common observe deviations from the predictions of a homogeneous model, Nb-oxide barriers being most-investigated example. discussing these shortcomings, high local nearly transparency instead tunneling probability order ${10}^{\ensuremath{-}8}$ an often concept. We here present experimental results Ag/Nb and Ag/Ta junctions which, in addition commonly observed finite zero-bias conductance, show pronounced, characteristic magnetic field dependence. A theory developed basis Bogoliubov-de Gennes equations which takes into account influence shielding current as well quasiparticles nonperpendicular incidence, typical for inhomogeneous transparency. The effect due non-normal incidence antisymmetric respect gap voltage. Below $\frac{\ensuremath{\Delta}}{e}$ positive resonant transmission to, Pincus-type bound states appearing quasiparticle momenta antiparallel current. Above $\frac{\ensuremath{\Delta}}{e}$, compensating negative contribution obtained. are quantitatively discussed their dependence angular spreading injection. find good agreement experiments broad distribution injected quasiparticles, Furthermore differences by magnitude between Nb-and Ta-based can be fully accounted for. On other hand, strong confinement injection forward direction ideal, barrier, marked experiment. Thus, we conclude transmission,