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 rho of both LaFeAsO1-xFx and SmFeAsO1-xFx 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 rho of the normal state which is reminiscent of the spin-density wave (SDW) signature in the parent material. At higher doping levels rho of LaFeAsO1-xFx 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 SmFeAsO1-xFx where superconductivity is enhanced and vanish when superconductivity is reduced in the doping region with Fermi-liquid-like behavior. Copyright (C) EPLA, 2009