Critical current of a ballistic asymmetric SNSNS junction

Abstract

The critical current through an asymmetrically stacked, double superconductor-normal-metal-superconduct (SNS) junction is studied in the mesoscopic and ballistic regime. The asymmetry in such SNSNS junctions excludes any intuitive choice for the phase phi(2) of the middle superconductor S-2. We propose to determine phi(2) from the condition that the currents in the two normal regions are the same. The Bogoliubov-de Gennes equation is solved analytically within the Andreev approximation. In the long S2 limit, we find that the current-phase relation (CPR) can be constructed directly from the CPRs of the two constituent SNS junctions, of which the longer SNS junction imposes a cutoff to the critical current. In short S-2 cases, the cutoff feature remains, but the cutoff value is affected by the Andreev-level tunneling. The dependencies of the SNSNS critical current on the length of S-2, and the asymmetry in the configuration are studied. (C) 1998 Elsevier Science Ltd. All rights reserved.