Competing orders and spin-density-wave instability in La(O(1-x)F(x)) FeAs

The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable T(c) = 26K in Fe-based oxypnictide La(O(1-x)F(x)) FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that a spin-density-wave (SDW) state develops at low temperature, in association with electron Nematic order. The electron-doping by F suppresses the SDW instability and induces the superconductivity. Therefore, the La(O(1-x)F(x)) FeAs offers an exciting new system showing competing orders in layered compounds. Copyright (C) EPLA, 2008.