Orbitally Resolved Quasiparticle Weight Renormalization Factors in Fe-based Superconductors.

We study the quasiparticle weight renormalization via spin and charge fluctuations in Fe-based pnictides within a multi-orbital tight-binding model with on-site interactions treated in weak coupling theory. The leading contribution to the quasiparticle scattering is calculated from the second-order self-energy diagram with the polarization operator calculated in the random-phase approximation. We find one-particle renormalization factors for orbital weights on each Fermi sheet, from the first order frequency derivative of the real part of the dynamic self-energy at the Fermi level. The orbitally resolved renormalization factor Z modifies the spin-fluctuation pairing through suppression of pair scattering processes in the corresponding orbital channel, resulting in orbital-selective Cooper pairing of electrons. We use the modified spin-fluctuation pairing interaction to compare our results with experimentally observed anisotropic gap structures of certain Fe-pnictides, to test the validity of current phenomenological theories of orbitally selective spin fluctuation pairing.