MgB 2 nanobridges were fabricated by e-beam lithography and Ar-ion beam milling. Nanobridges of widths ranging from 60 nm to 1μm and 3μm in length were realized by Ar-ion beam milling using amorphous carbon as etching mask. The processing did not harm the superconducting properties appreciably. High values of the critical current density, more than 10MA∕cm2, were measured for bridges with widths down to 60 nm. Current-voltage (I-V) characteristics showed a behavior typical of a bridge going normal, after the critical current is exceeded, and remaining normal as the current is decreased to a lower switch back value due to Joule heating. We could also observe switching behavior in some bridges indicating formation of normal hotspots in the bridges before they returned to their superconducting state. Alternative explanations may include natural grain boundaries in the film or the movement of Abrikosov vortices. The current-voltage (I-V) characteristics showing critical current densities up to 5×107⁢A∕cm2 indicates excellent film properties in the nanobridges.

We report on Josephson effects in Josephson junctions fabricated from magnesium diboride (MgB 2 ) thin films using a focused ion beam (FIB) milling technique. The films were deposited on SrTiO 3 (100) and Al 2 O 3 (1 102) substrates at room temperature using e-beam evaporation of MgB 2 with a post-annealing stage in Mg vapour. Conventional photolithography and Ar-ion-beam milling were used to pattern the films into 4 and 8 µm wide microbridges. A focused ion beam was used to narrow the microbridges to 2 µm. The narrowed microbridges were thinned by making 50 nm wide cuts across them. The depth of each cut was calibrated to remove 75% of the film thickness. A thin MgB 2 layer remained on the substrate after this process. The current-voltage (I -V ) characteristics of junctions made using this technique show that the junctions carry excess current. The first Shapiro step was observed when one of the junctions was irradiated with a microwave field of frequency f = 8.92 GHz. The Shapiro step appeared at a voltage value V = h f /2e = 18.445 µV.

MgB 2 ∕ Pd ∕ Fe ∕ Nb Josephson junctions were fabricated and characterized. The junctions exhibited the Josephson effect. A supercurrent was observed across the magnetically active layer formed at the Pd and Fe interface and also across the magnetic metal Fe itself. Shapiro steps and fractional Shapiro steps were observed when microwave fields were applied to the junctions. Modulation of the critical currents of the junctions was observed when an external magnetic field was applied in the plane of the junctions. The maxima of the magnetic field dependence of the critical current (Ic−B) did not occur at zero fields but at small positive fields of about 3.7μT. The magnetic field of 3.7μT increased the critical current by 100% when it was applied in the plane of the junction or perpendicular to the junction plane. The effect disappeared when the polarity of the field was reversed.

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