Abstract
Using cluster-perturbation theory, we calculate the spectral density A(k,ω) for a nematic phase of models describing pnictide superconductors, where very short-range magnetic correlations choose the ordering vector (π,0) over the equivalent (0,π) and thus, break the fourfold rotation symmetry of the underlying lattice without inducing long-range magnetic order. In excellent agreement with angle-resolved photoemission spectroscopy (ARPES), we find that the yz bands at X move to higher energies. When on-site Coulomb repulsion brings the system close to a spin-density wave (SDW) and renormalizes the bandwidth by a factor of ≈2, even small anisotropic couplings of 10–15 meV strongly distort the bands, splitting the formerly degenerate states at X and Y by ≈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 experiments. We find that orbital weights near the Fermi surface provide a better characterization than overall orbital densities and orbital polarization.
