Iron-based superconductors

Abstract

The iron-based superconductors (Fe-SCs) comprise a big family having the highest Tc = 55 K. In this family, an indispensable element is the typical magnetic element Fe, and except for the layer structure the characteristic electronic parameters are largely different from those in the cuprates. The discovery of this family, therefore, evidences that there are more than one route to finding high-Tc materials with Tc higher than 50 K. The parent compounds are antiferromagnetic metals, and both chemical substitution (doping) and application of pressure induce superconductivity. Like the cuprates, Fe-SCs show unconventional pairing, suggesting that strong electronic correlations play a major role in the pair formation. The strong correlations and high Tc have a root in the unique characteristics of the common building block composed of Fe and As (Se) layers in which an unusual antiferromagnetic state is also formed. Tc is material dependent, but the maximum Tc reaches around 50 K in most of sub-families after optimization, and never exceeds 55 K. For further enhancement of Tc, it may be needed to prepare an additional pairing channel by fabricating a novel structure.