Status of Iron Based Superconductors: Characteristics and Relevant Properties for Applications

Since the discovery of iron-based superconductors (IBSs) on LaFePO in 2006, many types of IBSs have been fabricated. IBSs have usually been compared to cuprates and MgB₂, and the methodology of research developed by them have been implemented to IBSs. As a result, many similarities between IBSs and cuprates have been revealed, e.g., the parent compounds being antiferromagnets and grain boundaries being weak-links to some extent. On the other hands, the distinct features of IBSs are highlighted as multiband superconductors (i.e., the 5 bands of Fe 3$d$ orbital crossing Fermi level) and extended $s$–wave symmetry. Additionally, some of the IBSs are topological superconductors that can be possible platforms for quantum computing. In this paper, an overview of IBS research and development in the last 18 years will be reported, involving characteristics of IBSs as well as strategies of increasing the superconducting transition temperature and critical current density.