Fabrication and characterization of Fe(Se,Te) Josephson devices and nanostrips

We report on recent results on Josephson junctions and dc-SQUIDs made by using Fe(Se,Te) chalcogenide superconductor. Josephson devices have been fabricated on SrTiO3 bicrystal substrates. The ratio of critical current densities of Josephson-like junctions to the critical current density of the bare film decreases for misorientation angles from 0 degrees up to 24 degrees. For larger angles, this ratio stays constant. As expected, the absolute critical current values depend strongly on the thin film quality. As a general occurrence, the reproducibility of electrical parameters is generally low for different thin film fabrications, even if the bare films show the same transition temperature and they are fabricated following the same procedure. Finally, an analysis of vortex creep motion in Fe(Se,Te) nanostrips is presented. The pinning energy of self-generated vortices ha has been derived from experiments in narrow strips. The analysis reveals the -need of including an additional energy term due to the interaction of vortex-antivortex that, with the narrowing of the strip widths, cannot be neglected.