SUPERCURRENT FLOW-THROUGH AN EFFECTIVE DOUBLE-BARRIER STRUCTURE

Supercurrent flow is studied in a structure that in the Ginzburg-Landa u regime can be described in terms of an effective double-barrier pote ntial. In the limit of strongly reflecting barriers, the passage of Co oper pairs through such a structure may be viewed as a realization of resonant tunneling with a rigid wave function. For interbarrier distan ces smaller than d(0) = pi xi(T) no current-carrying solutions exist. For distances between d(0) and 2d(0), four solutions exist. The two sy mmetric solutions obey a current-phase relation of sin(Delta phi/2), w hile the two asymmetric solutions satisfy Delta phi = pi for all allow ed values of the current. As the distance exceeds nd(0), a group of fo ur solutions appears, each containing (n-1) soliton-type oscillations between the barriers. We prove the inexistence of a continuous crossov er between the physical solutions of the nonlinear Ginzburg Landau equ ation and those of the corresponding linearized Schrodinger equation. We also show that under certain conditions a repulsive delta function barrier may quantitatively describe a superconductor-normal-supercondu ctor (SNS) structure. We conclude that the critical current of a SNSNS structure vanishes as root T'(c)-T, where T'(c) is lower than the bul k critical temperature.