CURRENT-PHASE RELATION OF A BALLISTIC ASYMMETRIC DOUBLE SUPERCONDUCTOR-NORMAL-METAL-SUPERCONDUCTOR JUNCTION

The zero-temperature current-phase (I-phi) relation (CPR) of a mesosco pic, ballistic, and asymmetrically stacked, double superconductor-norm al-metal-superconductor (SNS) junction is studied. Here phi is the pha se difference between the two superconducting end-electrodes. The lack of configuration symmetry in such asymmetric SNSNS junctions forbids a simple choice of values for the phase phi(2), of the middle supercon ductor. We propose to determine the values of phi(2), by equating the currents in the two normal regions. Two features in the CPR are found. First, the CPR of the asymmetric junction has a cutoff feature, whose origin is best demonstrated in the long middle superconductor (large L-2) cases, when the critical current of the double SNS junction is bo unded by the SNS junction that has the longer normal region. This cuto ff feature is more pronounced for longer L-2 and for higher degree of junction asymmetry. Second, in regions other than the cutoff region, t he CPR of the asymmetric junction deviates only within a few percent f rom the CPR of the symmetric junction which has the same total length L-Total in the normal regions and the same L-2. This is in contrast wi th the greater sensitivity the CPR has to the changes in L-Total or L- 2. (C) 1998 Elsevier Science B.V. All rights reserved.