Josephson junctions between a FeAs-based superconductor with antiphase $s$-wave pairing and a conventional $s$-wave superconductor are studied. The translational invariance in a planar junction between a single crystal pnictide and an aluminum metal greatly enhances the relative weight of electron pockets in the pnictide to the critical current. In a wide doping region of the pnictide, a planar and a point contact junction have opposite phases, which can be used to design a trijunction ring with $\pi$ phase to probe the antiphase pairing.

• Received 5 June 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.207001