Objectives

Thus within SUPER-IRON we plan to study a large amount of different compounds, belonging to different families (i.e. 1111, 122, 111 and 11) and also to new pnictide oxide superconductors. Samples in the form of single crystals, polycrystals, thin films, tapes and wires will be produced using different synthesis methods. The samples will be characterized by a large variety of techniques. The superconducting properties will be tuned by precisely controlled chemical substitutions, as well as by introducing a controlled amount of disorder through irradiation. The superconducting properties will be investigated in ideal systems (single crystals and epitaxial thin films) also under high magnetic field and/or pressure and compared with results on polycrystals.

A crucial issue to determine the power application potential is the ultimate limitation of the critical current related to the effect of grain boundaries. In order to find out whether pnictide GBs are really as strong current blockers as they are in HTSC, within this project clean GBs will be realized by growing thin films on bi-crystal substrates or by cutting single crystals by Focused Ion Beam (FIB). Spatial mapping of the local dissipation will be realized by a number of sophisticated techniques (scanning SQUID microscopy, scanning Hall probe microscopy, low temperature laser scanning microscopy), allowing direct investigations of the intrinsic limitations for the critical current.

This wide variety of experimental activities will be supported by intensive theoretical work including ab-initio calculations and theoretical modelling, with the aim of providing a positive feedback between theory and experiment. Phenomenological models will give information on the effect of impurities on superconducting properties, current flow, vortex dynamics and pinning properties. Ab-initio modelling of the electronic structure will allow a better understanding of the actual role of substitutions in these complex compounds and will provide input parameters for multiband analyses of superconducting and normal state properties. Furthermore, ab-initio calculations will be employed to understand and predict modifications of the electronic and magnetic properties at the interfaces, so as to provide the basis for the development of theoretical models for the suppression of superconductivity at the GBs.

The main objectives that we plan to achieve within this project can be summarized as follows:

• developing preparation methods of single crystals, thin films, and polycrystals;
• qualifying the ultimate potential of FeSCs for power applications, after optimization of sample quality and GB properties;
• comparing this potential with that of already existing superconductors (HTSC, MgB₂, Nb based superconductors).