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# Iron pnictides and chalcogenides: a new paradigm for superconductivity

## Abstract

Superconductivity is a remarkably widespread phenomenon that is observed in most metals cooled to very low temperatures. The ubiquity of such conventional superconductors, and the wide range of associated critical temperatures, is readily understood in terms of the well-known Bardeen–Cooper–Schrieffer theory. Occasionally, however, unconventional superconductors are found, such as the iron-based materials, which extend and defy this understanding in unexpected ways. In the case of the iron-based superconductors, this includes the different ways in which the presence of multiple atomic orbitals can manifest in unconventional superconductivity, giving rise to a rich landscape of gap structures that share the same dominant pairing mechanism. In addition, these materials have also led to insights into the unusual metallic state governed by the Hund’s interaction, the control and mechanisms of electronic nematicity, the impact of magnetic fluctuations and quantum criticality, and the importance of topology in correlated states. Over the fourteen years since their discovery, iron-based superconductors have proven to be a testing ground for the development of novel experimental tools and theoretical approaches, both of which have extensively influenced the wider field of quantum materials.

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## Acknowledgements

We thank all our co-authors and collaborators with whom we have had many discussions since the discovery of the iron-based superconductors. In particular, we thank H. Miao and T. H. Lee (Figs. 2 and 5), M. Christensen (Fig. 4) and L.-Y. Kong (Fig. 6) for their assistance in making some of the figures panels. R.M.F. was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division, under award number DE-SC0020045. A.I.C. acknowledges an EPSRC Career Acceleration Fellowship (EP/I004475/1) and the Oxford Centre for Applied Superconductivity (CFAS) for financial support. A.I.C. is grateful to the KITP programme ‘correlated20’, which was supported in part by the National Science Foundation under grant number NSF PHY-1748958. H.D. is supported by the National Natural Science Foundation of China (grant numbers 11888101 and 11674371), the Strategic Priority Research Program of the Chinese Academy of Sciences, China (grant numbers XDB28000000 and XDB07000000) and the Beijing Municipal Science and Technology Commission, China (grant number Z191100007219012). I.R.F. was supported by the US Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. P.J.H. was supported by the US Department of Energy, Office of Basic Sciences under grant number DE-FG02-05ER46236. G.K. was supported by NSF DMR-1733071.

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Fernandes, R.M., Coldea, A.I., Ding, H. et al. Iron pnictides and chalcogenides: a new paradigm for superconductivity. Nature 601, 35–44 (2022). https://doi.org/10.1038/s41586-021-04073-2

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