ISS2011 Development of iron-based superconducting devices (original) (raw)

For the investigation of the superconducting properties of iron-based superconductors Josephson junctions as well as Andreev reflection studies are potential tools. Therefore, we prepared different kinds of junctions, based on transport in direction of c-axis and ab-plane, respectively. The first one was a planar hybrid superconductor-normal metal-superconductor (SNS') thin film junction for transport studies along the c-axis. We used a BaFe 1.8 Co 0.2 As 2 (Ba-122) thin film (thickness 80 nm) prepared by pulsed laser deposition (PLD) as base electrode and a lead indium alloy as counter electrode, while the normal metal (barrier) layer was formed by thin gold films. By tuning the thickness of the gold layer and the area of the tunneling window, we were able to switch the behavior of our junction. For a thin gold layer ( 5 nm) and greater areas, RCSJ-like Josephson behavior can be observed with a radiation dependent excess current and nearly linear temperature dependence of the critical current. Increasing the thickness of the gold layer to 10 nm leads to conductance spectra, which are dominated by Andreev reflection and which show no remaining sign of Josephson effects. Secondly, an edge-type junction for transport measurements in the ab-plane of the pnictide layer, was prepared. It also is realized with PbIn as counter electrode, but with no artificial thin film. The temperature dependent conductance spectra showed some interesting features, which cannot be described within usual theoretical models. We introduced a third geometry, phase-sensitive corner junctions, which could ultimately test the pairing symmetry of Ba-122, if it is s ± type.