Magnetism and Superconductivity in Iron-based Superconductors Decided by   Condensed Particle-hole Excitations away from the Fermi Level
  The origin of magnetism and superconductivity in iron-based superconductors is still unclear. Here, by investigating the momentum-dependent particle-hole excitations which quantify the tendency of itinerant electrons towards various magnetic states or superconducting phases, we unravel a novel origin to account for the variety of physical properties of iron-based compounds. We show that condensation of particle-hole excitations away from the Fermi surface in momentum space is the underlying mechanism in deciding the magnetic and superconducting properties of iron-based materials. The applicability of this scenario to the whole family of iron-based superconductors suggests that inclusion of the orbital degrees of freedom, which may lead to competing tendencies towards different magnetically ordered states, is more crucial than taking into account the strong correlations. Our findings further indicate that in order to properly model these materials, the electronic states away from the Fermi level have to be considered. 
Ming-Cui Ding, Hai-Qing Lin, Yu-Zhong Zhang
cond-mat.supr-con cond-mat.mtrl-sci