Direct writing of low Tc superconductor-normal metal-superconductor junctions using a focused ion beam

Using a focused ion beam, we have produced superconductor-normal metal-superconductor junctions by controllably removing a portion of the top layer of a patterned superconductor-normal metal thin film. The high-quality junctions showed Josephson coupling which scaled qualitatively with barrier properties and temperature as expected. The largest product of a junction’s critical current and the normal state resistance measured is 98 μV at 4.2 K. The method has good reproducibility and could be exploited in a number of superconducting electronics applications.