Observation of the Josephson effect in Pb/Ba1-xKxFe2As2 single crystal junctions.

We have fabricated c-axis Josephson junctions on single crystals of Ba1-xKxFe2As2 by using Pb as the counterelectrode in two geometries, planar and point contact. Junctions in both geometries show resistively shunted junction I-V curves below the T{C} of the counterelectrode. Microwave induced steps were observed in the I-V curves, and the critical currents are suppressed with an in-plane magnetic field with well-defined modulation periods indicating that the Josephson current is flowing in a manner consistent with the small to intermediate sized junction limit. I{C}R{N} products of up to 0.3 mV have been observed in these junctions at 4.2 K. The observation of Josephson coupling along the c axis between Ba1-xKxFe2As2 and a conventional superconductor suggests the existence of an s-wave symmetry in this class of iron pnictide superconductors.