Electronic, Magnetic, and Superconducting Properties of FeAs Supercond…

Discovery of superconductivity in LaFePO in 2006 and LaFeAsO in 2008 opened a new family of superconductors, namely, FeAs or iron-based superconductors. This family of new superconductors has exotic physical properties. They have quasi-two-dimensional electronic structures with multiple Fermi surfaces, and superconductivity appears at the vicinity of antiferromagnetism. Comparison of electronic energy dispersions from the density functional calculations and those from the angle-resolved photoemission spectroscopy shows that electronic energy dispersions are renormalized by many-body effects. Normal-state electronic structures of FeAs superconductors are qualitatively described by standard density functional theory (DFT) while it is claimed that the mass renormalization is quantitatively described by DFT+DMFT. Magnetic ordering is well described by DFT and it is due to local magnetic moments governed by Heisenberg Hamiltonian rather than spin-density wave due to Fermi-surface nesting. Local magnetic moments are larger than ordered magnetic moments, existing even in nonmagnetic phase. We perform first-principles calculations of electronic and magnetic properties of FeAs superconductors with various spin configurations to obtain magnetic exchange couplings of Fe magnetic moments. We discuss superconducting properties using a modified Eliashberg theory based on material parameters from DFT. This work is supported by the NRF of Korea (Grant No.2011-0018306). Computational resources have been provided by KISTI Supercomputing Center (Project No. KSC-2013-C3-062).