BALLISTIC JOSEPHSON-CURRENT FLOW-THROUGH AN ASYMMETRIC SUPERCONDUCTOR NORMAL-METAL SUPERCONDUCTOR JUNCTION

We study the Josephson current through a ballistic, normal metal, mesoscopic, one-dimensional quantum channel in contact with two superconducting electrodes. The two superconductors have different energy gaps DELTA1 and DELTA2. Increasing either energy gap increases the critical current I(c). This enhancement of I(c) results from altering the mesoscopic processes which control the Josephson-current flow, rather than through the proximity effect. The effect is strongest in junctions shorter than the size of a Cooper pair. When the asymmetry is large, such that DELTA2 much greater than DELTA1, we find the critical current can be several times larger than its bulk value in the weaker superconductor, namely, I(c) > eDELTA1/hBAR.