Electrodynamic response of incoherent metals: Normal phase of iron pnictides

The recent discovery of high-temperature superconductivity in doped iron pnictides is the latest example of unanticipated behavior exhibited by d- and f-band materials. The symmetry of the superconductor (SC) gap, along with the mechanism of its emergence from the normal state, is a central issue in this context. Here, motivated by a host of experimental signatures suggesting strong correlations in the Fe pnictides, we undertake a detailed study of their normal state. Focusing on symmetry-unbroken phases, we use the correlated band-structure method, local density approximation plus dynamical mean-field theory (LDA+DMFT), to study the one-particle responses of both LaO1-xFeAsFx and SmO1-xFeAsFx in detail. Basing ourselves on excellent quantitative agreement between LDA+DMFT and key experiments probing the one-particle responses, we extend our study, undertaking the first detailed study of their normal-state electrodynamic response. In particular, we propose that near-total normal-state incoherence, resulting from strong, local correlations in the Fe d shell in Fe pnictides, underpins the incoherent normal-state transport found in these materials, and discuss the specific electronic mechanisms leading to such behavior. We also discuss the implications of our work for the multiband nature of the SC by studying the pairing glue function, which we find to be an overdamped electronic continuum. Similarities and differences between cuprates and Fe pnictides are also touched upon. Our study supports the view that SC in Fe pnictides arises from a bad-metallic incoherent normal state that is proximate to a Mott insulator.