Spin-orbit Coupling in Five-Orbital Model for Iron Pnictides

The effect of spin-orbit coupling on the band structure and Fermi surface in the five-orbital model for iron-based superconductors is studied. Since there are two iron ions in the unit cell and their orbitals indirectly coupled through as orbitals, we introduce the constants of the intra- and inter-ion spin-orbit coupling in the effective model to separate the effect of the corresponding contributions on the band structure. We show that the intra- and inter-ion parts of the spinorbit coupling lead to Fermi surface topology change – splitting of the four contours of the Fermi surface around the point M = (π, π).