Josephson effects at iron pnictides - phase-sensitive experiments

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The electrical transport in the pnictides especially the quasiparticle tunneling and Josephson effects will be studied in inhomogeneous superconducting systems. The symmetry of the order parameter will be determined and the consequences for the Josephson behaviour will be discussed. Different kinds of Josephson junctions with pnictide electrodes including new types in comparison to the known low and high Tc superconductors will be realized and their properties will be experimentally studied in detail. These investigations will lead to a better understanding of fundamental properties of the pnictides as well as to a realistic judgement on the potential for applications of pnictides in superconducting electronics and sensor applications. The interdisciplinary orientation of the project leads to a strong interaction with chemical and materials science groups (polycrystalline samples, single crystals and thin films of different pnictides). Their pnictide samples will be used in this project to prepare different kinds of Josephson junctions (e.g. hybrid junctions with one electrode of a conventional s-wave superconductor, new kinds of phase-sensitive corner junctions, all-pnictide junctions where both electrodes are pnictide superconductors). Experimental properties of the realized junctions will be analyzed ( e.g. currentvoltage characteristics, microwave response, current-physe relations, dependencies on temperature and external magnetic field) and compared to well-known Josephson junctions and new theories taking into account the special properties of the pnictides. In this way important parameters to characterise the pnictide samples and for further optimization of the preparation process will be give back to the preparation groups. In cooperation with theory groups the interpretation of the experimental results will be improved. The network within the SPP will be forced by the comparison to experimental results from other groups (regarding the symmetry of the pairing, the current transport across grain boundaries, measurements on planar FeSe thin film tunnel junctions) and additional investigations on the junctions prepared in this project in other groups (e.g. THz response and emission).