Study of non-Fermi-liquid-like state and pairing symmetry in iron pnictides based on the multiorbital Hubbard-Holstein model

We study the five-orbital Hubbard-Holstein model, taking account of the electron-phonon (e-ph) interaction due to the Fe-ion oscillation. In order to include the self-energy correction, we employ the fluctuation exchange (FLEX) approximation. It is revealed that the orbital fluctuations are enhanced by the e-ph interaction, which causes a strong attractive pairing interaction. The orbital fluctuations give rise to highly anisotropic quasiparticle lifetime (hot/cold spot structure) and non-Fermi-liquid-like transport phenomena. From the phase diagram obtained by the FLEX approximation, we find that (i) s-wave state without sign reversal is stable for the moderate e-ph coupling in the broad parameter region, which is consistent with the experimental non-magnetic impurity effect, (ii) the renormalization induced by the orbital fluctuation is not so strong, and (iii) superconducting (SC) state with node can appear in the broad parameter region in the presence of impurities.