Loss of π-junction behavior in an interacting impurity Josephson junction

Using a generalization of the noncrossing approximation which incorporates Andreev reflection, we study the properties of an infinite-ii Anderson impurity coupled to two superconducting leads. In the regime where Delta and T-K are comparable, we find that the position of the subgap resonance in the impurity spectral function develops a strong anomalous phase dependence-its energy is a minimum when the phase difference between the superconductors is equal to pi. Calculating the Josephson current through the impurity, we find that pi-junction behavior is lost as the position of the bound state moves above the Fermi energy.