Superconducting MgB2 weak links and superconducting quantum interference devices prepared by AFM nanolithography

Smooth MgB2 superconducting thin films with roughness below 10 nm, critical temperature Tc = 31 K and critical current density jc (4.2 K) ≈ 5 × 106 A/cm2 were prepared by magnetron sputtering and ex-situ annealing in vacuum. On these films, weak links and radio frequency superconducting interference devices were prepared by combination of optical lithography and AFM scratching as well as by focused ion beam milling. Phase and current-phase characteristics have been investigated on our superconducting quantum interference devices.