The intrinsic electronic phase diagram of iron-oxypnictide superconductors

We present the first comprehensive derivation of the intrinsic electronic phase diagram of the iron-oxypnictide superconductors in the normal state based on the analysis of the electrical resistivity ρ of both LaFeAsO_{1- x}F_x and SmF eAsO_{1- x}F_x for a wide range of doping. Our data give clear-cut evidence for unusual normal-state properties in these new materials. In particular, the emergence of superconductivity at low doping levels is accompanied by distinct anomalous transport behavior in ρ of the normal state which is reminiscent of the spin-density wave (SDW) signature in the parent material. At higher doping levels ρ of LaFeAsO_{1- x}F_x shows a clear transition from this pseudogap-like behavior to Fermi-liquid–like behavior, mimicking the phase diagram of the cuprates. Moreover, our data reveal a correlation between the strength of the anomalous features and the stability of the superconducting phase. The pseudogap-like features become stronger in SmF eAsO_{1- x}F_x where superconductivity is enhanced and vanish when superconductivity is reduced in the doping region with Fermi-liquid–like behavior.