Planar MgB ₂ superconductor-normal metal-superconductor Josephson junctions fabricated using epitaxial MgB ₂/TiB ₂ bilayers

We have fabricated planar superconductor-normal metal-superconductor Mg B2 Josephson junctions using Ti B2 as the barrier material. On a bilayer film of Mg B2 Ti B2 on SiC substrate, Mg B2 was locally removed to create a gap of ≤50 nm, separating the Mg B2 film into two electrodes. A Josephson coupling is established through the Ti B2 film across the gap by proximity effect. The junctions exhibit resistively shunted junction like current-voltage characteristics up to 31 K. An ac Josephson effect was observed and the behavior of the Shapiro steps are in good agreement with theoretical predictions. The magnetic field modulation of the critical current also agrees with the thin film planar junction behavior.