Electronic structure of iron-based superconductors: from pnictides to chalcogenides and other similar systems

This review discusses and compares electronic spectra of new iron-based high-temperature superconductors (HTSC), as well as a number of chemically similar compounds. Particular attention is payed to iron chalcogenide K_{1-x}Fe_{2-y}Se_2, which is isostructural to BaFe_2As_2 (122) pnictide. It is shown, that Fermi surfaces of K_{1-x}Fe_{2-y}Se_2 are essentially different from those for pnictides. Using LDA+DMFT and LDA'+DMFT calculations we show, that electronic correlations in K_{1-x}Fe_{2-y}Se_2 influence the electronic structure much more significantly, than in the most studied 122 system. We also discuss the electronic structure of several multiple-band superconductors, chemically similar to iron-based HTSC, with relatively small values of $T_c$, such as SrPt_{2}As_{2}, APt_{3}P, (Sr,Ca)Pd_2As_2, and non superconducting compound BaFe_2Se_3. It is shown, that electronic structure of these systems is very different from previously studies iron pnictides and chalcogenides. The value of T_c in these systems can be understood within the simple BCS model.