0 and π phase Josephson coupling through an insulating barrier with magnetic impurities

We present the experimental evidence of the existence of the π state in the Josephson junction with magnetic impurities in the insulating barrier. We have studied temperature and field dependencies of the critical current IC in the Nb-Fe0.1Si0.9-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 π states within one tunnel junction takes place which leads to the appearance of a sharp cusp in the temperature dependence IC(T) similar to the IC(T) cusp found for the 0-π transition in metallic π junctions. This cusp is not related to the 0-π temperature induced transition itself, but is caused by the different temperature dependencies of the opposing 0 and π supercurrents through the barrier. (orig.)