The 0 and the pi phase Josephson coupling through an insulating barrier with magnetic impurities

Abstract

We have studied temperature and field dependencies of the critical current $I_{C}$ in the Nb-Fe$_{0.1}$Si$_{0.9}$-Nb Josephson junction with tunneling barrier formed by paramagnetic insulator. We demonstrate that in these junctions the co-existence of both the 0 and the $\pi$ states within one tunnel junction takes place which leads to the appearance of a sharp cusp in the temperature dependence $I_{C}(T)$ similar to the $I_{C}(T)$ cusp found for the $0-\pi$ transition in metallic $\pi$ junctions. This cusp is not related to the $0-\pi$ temperature induced transition itself, but is caused by the different temperature dependencies of the opposing 0 and $\pi$ supercurrents through the barrier.