Ironbased

Iron-based refers to materials in which iron is a key element, typically forming layered compounds with iron coordinated to pnictogen or chalcogen atoms. The most notable are iron-based superconductors, a class of high-temperature superconductors first reported in 2008 with LaFeAsO1−xFx showing Tc around 26 K, later raised to above 50 K in other derivatives and under pressure. The parent compounds generally show metallic or semimetallic behavior and exhibit antiferromagnetic order with a coupled structural transition; superconductivity emerges when this magnetism is suppressed by chemical substitution or pressure.

Structurally, many iron-based superconductors feature FeX layers where Fe forms a square lattice tetrahedrally coordinated by pnictogen or chalcogen atoms, separated by spacer layers that vary by family. The electronic structure is multi-band, dominated by Fe 3d states, leading to multiple Fermi surfaces. The leading pairing scenario is often described as sign-changing s-wave (s±) driven by spin fluctuations, although other symmetries have been proposed.

Critical temperatures in this family exceed 50 K in some compounds, and upper critical fields are generally high with moderate anisotropy, offering potential for applications if materials can meet practical current and defect requirements. Major families include 1111 (RFeAsO), 122 (AFe2As2), 111 (AFeAs), and 11 (FeSe, FeTe), among others and their doped or intercalated derivatives. Research continues into pairing mechanisms, phase diagrams, and materials engineering to improve performance.