Planar superconductor-normal-superconductor Josephson junctions in MgB2

We report the successful creation of planar MgB2 junctions by localized ion damage in thin (100 nm) films of MgB2 on sapphire by milling a 50 nm trench with a focused-ion beam across tracks of widths between 1 and 5 μm. When the depth of the trench is between 70% and 80% of the film thickness, devices show critical currents (IC) for temperatures below 25 K. The IC of these devices is strongly modulated by applied microwave radiation and magnetic field. The product of the critical current and normal state resistance (ICRN) is remarkably high, implying a potential for very-high-frequency applications.