Josephson effects in Josephson junctions, fabricated from thin films using a focused ion-beam milling technique, were reported. The films were deposited onto SrTiO3(100) and Al2O3(1¯1▪2) substrates at room temperature using the e-beam evaporation of MgB2, with a post-annealing stage in Mg vapour. Conventional photolithography and Ar-ion-beam milling were used to pattern the films into 4 and 8µm wide micro-bridges. A focused ion beam was used to narrow the micro-bridges to 2µm. The narrowed micro-bridges were thinned by making 50nm-wide cuts across them. The depth of each cut was calibrated to remove 75% of the film thickness. A thin MgB2 layer remained on the substrate after this process. The current–voltage characteristics of junctions made by using this technique showed that the junctions carried excess current. The first Shapiro step was observed when one of the junctions was irradiated with a microwave field of frequency 8.92GHz. The step appeared at a voltage of 18.445µV.

Josephson Effects in Magnesium Diboride Based Josephson Junctions. A.Malisa, M.Valkeapää, L.G.Johansson, Z.Ivanov: Superconductor Science and Technology, 2004, 17, S345-9