TUNNELING EFFECT OF COOPER PAIRS IN WEAK-LINK SUPERCONDUCTOR STRUCTURES WITH MULTI-JUNCTIONS UNDER THE CONDITION FOR OVERSTEPPING THE JOSEPHSON APPROXIMATION

Abstract

In this paper, tunneling effect of Cooper pairs in weak-link superconductor structure with multi-junctions under the condition for overstepping the Josephson approximation is discussed. The equations describing the electric current based on the tunneling effect of Cooper pairs in several kinds of weak-link superconductor structures with multi-junctions are obtained under the condition to overstep the Josephson approximation. For both SISISIS and a four junctions ring, when all junctions are in the zero voltage state, the exact solution of the equations is obtained. It is found that, because of the tunneling effect of the Cooper pairs, an alternating current exists which can be expressed by an elliptic function. For a four junctions ring, the relation between the period of the alternating current and flux is pointed out. At last, the condition for overstepping the Josephson approximation is discussed. The result shows that overstepping the Josephson approximation may be possible when the volumes of superconductors are small enough.