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Spectral density in a nematic state of iron pnictides

Using cluster-perturbation theory, we calculate the spectral density A(k,w) for a nematic phase of models describing pnictide superconductors, where very short-range magnetic correlations choose the ordering vector (pi,0) over the equivalent (0,pi) and thus break the fourfold rotation symmetry of the underlying lattice without inducing long-range magnetic order. In excellent agreement with angle resolved photo-emission spectroscopy (ARPES), we find that the yz bands at X move to higher energies. When onsite Coulomb repulsion brings the system close to a spin--density-wave (SDW) and renormalizes the band width by a factor of approx. 2, even small anisotropic couplings of 10 to 15 meV strongly distort the bands, splitting the formerly degenerate states at X and Y by approx. 70 meV and shifting the yz states at X above the chemical potential. This similarity to the SDW bands is in excellent agreement with ARPES. An important difference to the SDW bands is that the yz bands still cross the Fermi level, again in agreement with experiment. We find that orbital weights near the Fermi surface provide a better characterization than overall orbital densities and orbital polarization.