The Antiferromagnetic Phase of Iron-Based Superconductors

In the present chapter, we mainly focus on theoretical studies which adopt material specific model Hamiltonians that take into account the band structure obtained from first principles calculation. In particular, we pay special attention to the studies based on the models that consider all five of the Fe 3d bands. We first review the model construction from the first principles band calculation, and then describe the main features of the band structure and the Fermi surfaces. We then discuss how the many body interactions together with these peculiar band structures and Fermi surfaces result in the development of spin fluctuations or antiferromagnetism. As for the mechanism of superconductivity, we describe mainly the spin- fluctuation-mediated pairing, while we also comment on some other possibilities. Finally, we give a review on how the electronic states depend on the materials, affecting both the spin fluctuations and the superconductivity.