The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T c = 26 K in the Fe-based compound LaFeAsO1−x F x has been very enthusiastic. In short order, other Fe-based superconductors with the same or related crystal structures were discovered with T c up to 56 K. Many experiments were carried out and theories formulated to try to understand the basic properties of these new materials and the mechanism for T c. In this selective critical review of the experimental literature, we distill some of this extensive body of work, and discuss relationships between different types of experiments on these materials with reference to theoretical concepts and models. The experimental normal-state properties are emphasized, and within these the electronic and magnetic properties because of the likelihood of an electronic/magnetic mechanism for superconductivity in these materials.