Superconductivity in the Fe-Pnictides - From first principle calculations to effective RG studies

The functional Renormalization Group (fRG) is used to determine the superconducting (SC) mechansim in the ferropnictides, with the main emphasis on distiguishing universal and material-specific aspects. To this end we use a five-band d-orbital whose interactions, in contrast to earlier fRG studies, are not taken as scalar model parameters, but calculated ``a priori'' from constrained RPA calculations. We universally find a SC pairing instability, driven by inter-Fermi surface (FS) scattering and resulting in a sign-changing s+- wave order parameter. However, the gap anisotropy is shown to be dependent on material-specific orbital parameter deviations not only by the ``non-interacting'' (i.e. LDA) part of the d-orbital Hamiltonian, but also by self-energy corrections.