Breaking of four-fold lattice symmetry in a model for pnictide   superconductors
  We investigate the interplay of onsite Coulomb repulsion and various mechanisms breaking the fourfold lattice symmetry in a three-band model for the iron planes of iron-based superconductors. Using cluster-perturbation theory allows us to locally break the symmetry between the x- and y-directions without imposing long-range magnetic order. Previously investigated anisotropic magnetic couplings are compared to an orbital-ordering field and anisotropic hoppings. We find that all three mechanisms for a broken rotational symmetry lead to similar signatures once onsite interactions are strong enough to bring the system close to a spin-density wave. The band distortions near the Fermi level are independent of differences between the total densities found in xz and yz orbitals. 
Maria Daghofer and Andr\'e Fischer
cond-mat.supr-con cond-mat.str-el