Layered iron pnictide superconductors: Discovery and current status

Abstract

On February 23, 2008, our paper reporting Tc of 26K in LaFeAsO 1-xFx was published on line in the Journal of American Chemical Society. The present article describes our research flow to this discovery and summarizes research advances on Fe (Ni)-based superconductors since then. Emphases are placed on that (1) all the superconducting materials reported to date have square lattice of Fe ions whose 3d orbitals predominately contribute the Fermi level. (2) Occurrence of crystallographic transition from tetragonal phase to a lower symmetry phase is required for parent phases of high Tc. (3) There are a variety of materials with different chemical compositions as candidates for high Tc superconductors. Even Fe ions may be substituted by Co ion without drastically reducing Tc. Fabrication of epitaxial thin films of Co-substituted Sr(FeAs)2 exhibiting Tc=20K is also described. ©2008 The Physical Society of Japan.