High-temperature superconductivity in iron-based materials

The surprising discovery of superconductivity in layered iron-based materials, with transition temperatures climbing as high as 55 K, has led to thousands of publications on this subject over the past two years. Although there is general consensus on the unconventional nature of the Cooper pairing state of these systems, several central questions remain - including the role of magnetism, the nature of chemical and structural tuning, and the resultant pairing symmetry - and the search for universal properties and principles continues. Here we review the progress of research on iron-based superconducting materials, highlighting the main experimental benchmarks that have been reached so far and the important questions that remain to be conclusively answered.