The new age of iron-based superconductors
With the 2008 discovery of superconductors in materials based on iron, scientists had a second class of materials exhibiting the macroscopic quantum phenomenon of high-temperature superconductivity. The road to room-temperature superconductivity seemed to open up because of the possibility of comparing these with the famous cuprate superconductors. European and Japanese scientists came together on the EU-funded project SUPER-IRON (Exploring the potential of iron-based superconductors) to develop a roadmap to exploit FeSCs in power applications. FeSCs appear to exhibit several advantages, including less sensitivity to defects of current transmission across grain boundaries, when compared to conventional high-temperature superconductors. Extensive work was devoted to preparing FeSCs as single crystals, polycrystals, wires and thin films. Single crystal work led to optimised synthesis techniques for polycrystalline forms with improved superconducting properties. Researchers made significant progress in the fabrication of wires and thin films, with the most interesting results demonstrated on calcium fluoride (CaF2) substrates. The SUPER-IRON team confirmed the remarkable tunability of superconducting properties of thin films of iron chalcogenides Fe(Te, Se) on CaF2 by precisely controlled doping and through introduction of defects by neutron irradiation. They also prepared the first new iron arsenic-based superconducting wires using the ex situ power-in-tube method. Investigating the behaviour of the materials at grain boundaries is critical to their potential use in power applications. Researchers applied both experimental and theoretical techniques with several exciting results. The thin bicrystalline films produced on various substrates exhibited intergrain coupling better than cuprate semiconductors and exceeded all assessment criteria for power applications. The research initiated within the SUPER-IRON project will continue with the results from the theoretical tools developed to predict superconducting properties in different materials. Researchers hope to gain new insights into how electrons pair up and conduct electricity without dissipation and then apply that knowledge to cuprate superconductors. Experimental results and theoretical models are expected to provide answers to the questions that remain open regarding conventional high-temperature cuprate superconductors. SUPER-IRON was a research project and, therefore, immediate exploitation of its results was not envisaged, but the groundwork for future development of a roadmap for the exploitation of FeSCs in power applications has been laid.
Keywords
Iron-based superconductors, high-temperature superconductivity, cuprate semiconductors, power applications
