Non-local correlation effect in iron-based superconductors*

While experimental studies of many iron-based superconductors observe momentum-dependent effects like the so-called blue/red shift that describes oppposite energetic shifts of electron- and hole-parabolas with respect to bandstructure calculations, DMFT by construction is not able to capture such features. We therefore present a momentum-dependent and dynamical many-body method, the Two-Particle Self-Consistent (TPSC) approach, and apply it to an ab-initio-derived multi-orbital Hubbard model.
Multi-orbital TPSC assumes the irreducible interaction vertex to be an orbital-dependent constant, which is self-consistently determined from local spin and charge sum rules. Those are immediate representatives of the Pauli principle. We disentangle the contribution of non-local correlations in LiFeAs and show that in the local approximation, i.e. afer momentum-averaging the self-energy, one recovers dynamical-mean field theory (DMFT) results.
The comparison of our results to experimental data shows that non-local correlations in LiFeAs are decisive to describe the spectral function, Fermi surface and scattering rates.