Frontiers of Research on Iron-Based Superconductors toward Their Application

The recent discovery of iron-based superconductors has evoked enthusiasm for extensive research on these materials because they form the second high-temperature superconductor family after the copper oxide superconductors and impart an expectation for materials with a higher transition temperature ( T c ). It has also been clarified that they have peculiar physical properties including an unconventional pairing mechanism and superconducting properties preferable for application such as a high upper critical field and small anisotropy. This paper reviews the research on thin films, Josephson junctions, and superconducting wires and tapes made from iron-based superconductors, which has been performed toward the realization of future applications. Though there are many technical hurdles toward the practical application of these materials, some promising features such as a high critical current density in thin films under high magnetic fields and advantageous grain boundary properties over copper oxides have been clarified.