Iron based chalcogenide and pnictide superconductors: From discovery to chemical ways forward

Iron-based superconductors are interesting due to their intrinsic magnetism, which often precedes superconductivity. Since 2008, advances have attempted to resolve this apparent but non-obvious link. This has resulted in growing evidence that iron based compounds, especially those containing Fe-X (X = Group15 element) and Fe–Y (Y = Group16 element), have similarities in their superconducting behavior (despite structural dissimilarities). Synthesis of these phases is hence critical in furthering understanding of superconductivity in these systems. Particularly, controlling crystal lattice strain is identified as path towards increasing transition temperature in iron based superconductors. Here highlight factors that are of immediate and future challenges of relevance for these materials. For researchers in these fields, an accessible description of the solid state and structural chemistry of these systems is provided. Phenomena discussed here include (i) spin/orbital fluctuations, (ii) nematicity (iii) vacancy ordering, and (iv) magnetism. These are composition and hence synthesis dependent. Synthetic controls in the case of low dimensional and layered chalcogenide and pnictide superconductors are duly elucidated. It may be noted that just like Fe; X, Y are oftentimes earth abundant elements, making this category of materials prospectively relevant for future applications. We expect pointers provided here to aid multidisciplinary research on iron based superconductors.