Josephson effect between electron-doped and hole-doped iron pnictide single crystals

We have observed the Josephson effect in junctions formed between single crystals of $SrFe1.74Co0.26As2$ and $Ba0.23K0.77Fe2As2$⁠. The ac Josephson effect was observed under microwave irradiation in the $I-V$ characteristics. By applying an in-plane magnetic field, the critical current is completely modulated and shows a relatively symmetric diffraction pattern consistent with the intermediate junction limit. The observation of the Josephson effect in the $p-n$ bicrystal structure not only has significant implications for designing phase-sensitive junctions to probe the pairing symmetry of iron pnictide superconductors, but also represents an important step in developing all iron pnictide devices for applications.