I-V Curves of Superconducting Microconstrictions

摘要

In recent years there has been much experimental and theoretical work on small-area high-current-density superconducting junctions, since such junctions have advantages for certain practical applications. Although the I-V curve properties of classic (high barrier) tunnel junctions have long been understood in great detail, the properties of metallic (no barrier) junctions have been studied only more recently and in less detail, and the transitional case (small barrier) has received practically no attention at all. Here the authors present a new unified treatment which is sufficiently general to embrace both limits, as well as the intermediate regime. In this work, they confine their attention primarily to the N-S interface within the context of a genralized Andreev reflection model. This avoids the complications of the Josephson effect, while allowing for the complete delineation of the I-V curves including the so-called excess current at high voltages, as it increases from zero in tunnel junctions to lits limiting value in clean metallic contacts. In addition, by suitably joining two N-S interfaces together as a model for the S-S interface, the authors have discovered a physically plausible explanation for the subharmonic energy gap structure that has been observed in the I-V curves of a wide variety of microconstrictions.