Nematic state in iron pnictides

Abstract

Iron pnictides, discovered in 2008, are the second family of high temperature superconductors, cuprates being the first. In both families the mechanism of superconductivity is unknown. As cuprates, superconductivity emerges upon doping a magnetic state. However, there are also important differences between the two families. Cuprates present (¿,¿) magnetism while the magnetism in pnictides is (¿,0), i.e antiferromagnetic in the x-direction while ferromagnetic in the y-direction. Pnictides present a structural phase transition that together with the antiferromagnetic transition encloses a nematic phase (see Fig. 1). Nematicity has also been found in cuprates but without the presence of the structural transition. The nematic phase is characterized by an x/y anisotropy and it has been observed by many experimental techniques concluding that it is electronic in origin. It is believed that magnetism and nematicity are key to understand the mechanism of superconductivity[1].