Grain boundary junctions of FeSe0.5Te0.5 thin films on SrTiO3 bi-crystal substrates

Grain boundary junctions were fabricated in the epitaxial FeSe0.5Te0.5 thin films on [001] tilt SrTiO3 bi-crystal substrates with a CeO2 buffer layer. Critical current densities across the junctions with different mis-orientation angles of 4°, 7°, 15°, and 24° were measured at magnetic fields up to 30 T. It was found that the 4° and 7° junctions carry critical current densities comparable to that of the intra-grain film while those of the 15° and 24° junctions were suppressed drastically. A critical mis-orientation angle of around 9° was identified that separates the strong coupling region from the weak link region. We found that the critical current densities across the grain boundary with a 24° mis-orientation angle are modulated by the magnetic field, indicating a Josephson Effect. This junction is estimated to be in the intermediate-size regime with an effective transverse junction width L ∼ 2.6–2.8 μm and a Josephson penetration depth λJ ∼ 1.2 μm.