Supercurrent flow through an effective double-barrier structure.

Supercurrent flow is studied in a structure that in the Ginzburg-Landau regime can be described in terms of an effective double barrier potential. In the limit of strongly reflecting barriers, the passage of Cooper pairs through such a structure may be viewed as a realization of resonant tunneling with a rigid wave function. For interbarrier distances smaller than d0 = πξ(T ) no current-carrying solutions exist. For distances between d0 and 2d0, four solutions exist. The two symmetric solutions obey a current-phase relation of sin(∆φ/2), while the two asymmetric solutions satisfy ∆φ = π for all allowed values of the current. As the distance exceeds nd0, a new group of four solutions appears, each contaning (n − 1) soliton-type oscillations between the barriers. We prove the inexistence of a continuous crossover between the physical solutions of the nonlinear Ginzburg-Landau equation and those of the corresponding linearized Schrödinger equation. We also show that under certain conditions a repulsive delta function barrier may quantitatively describe a SNS structure. We are thus able to predict that the critical current of a SNSNS structure vanishes as √ T ′ c − T , where T ′ c is lower than the bulk critical temperature. 74.20.De, 74.50.+r, 74.60.Jg, 74.62.-c, 74.80.Fp Typeset using REVTEX