Effect of hybridization on structural and magnetic properties of iron-based superconductors

We show that the strong hybridization between the iron 3d and the arsenic 4p orbitals, in the newly discovered iron-based high-T-c superconductors, leads to an explanation of certain experimental observations that are presently not well understood. The existence of a lattice distortion, the smallness of the Fe magnetic moment in the undoped systems, and the suppression of both the lattice distortion and the magnetic order upon doping with fluorine, are all shown to result from this hybridization. We show that, as a result of hybridization, a tetragonal-to-orthorhombic distortion lowers the electronic energy of the Fe ions. The ground state of the Fe ions is shown to be a mixture of five states, four of which have zero magnetic moment, causing a large reduction in the average value of the magnetic moment per Fe site.