Superconductivity in iron compounds

TLDR

The discovery of superconductivity at 26 K in fluorine‑doped LaFeAsO sparked worldwide interest in iron pnictide and chalcogenide superconductors, whose Fe‑derived Fermi surfaces and rapidly changing Fermiology give rise to unconventional normal and superconducting properties that are closely linked to magnetism and leave open questions about nodal structure. This review seeks to organize the extensive and seemingly disparate data on Fe‑based superconductors in order to reveal correlations and underlying explanations. It does so by providing an overview of the materials and their superconductivity, drawing on numerous references to highlight key findings.

Abstract

Kamihara and coworkers' report of superconductivity at ${T}_{c}=26\text{ }\text{ }\mathrm{K}$ in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled ``conventional'' superconductors. Clearly, superconductivity and magnetism or magnetic fluctuations are intimately related in the FePn/Ch, and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With ${T}_{c}$ values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review provides an overview, using numerous references, with a focus on the materials and their superconductivity.