Josephson coupling through a magnetic impurity

We analyze nonperturbatively the behavior of a Josephson junction in which two BCS superconductors are coupled through an Anderson impurity. We recove r earlier perturbative results which found that a delta = pi phase differen ce is preferred when the impurity is singly occupied and the on-site Coulom b interaction is large. We find a novel intermediate phase in which one of delta = 0 and delta = pi is stable while the other is metastable, with the energy E(delta) having a kink somewhere in between. As a consequence of the kink, the I-V characteristics of the junction are modified at low voltages . [S0031-9007(99)08784-0].