Competing orders and spin-density-wave instability in La(O _1−x F _x )FeAs

TLDR

The interplay between superconducting, charge, and spin ordered phases is a central topic in condensed matter physics. The study investigates whether the 150 K resistivity anomaly in LaOFeAs arises from a spin‑density‑wave instability and whether fluorine doping suppresses this SDW to recover superconductivity. The authors combine experimental measurements with theoretical modeling to demonstrate that the anomaly originates from a spin‑density‑wave instability, which is quenched by fluorine doping, thereby restoring superconductivity. The results confirm that the 150 K anomaly is a spin‑density‑wave instability suppressed by fluorine doping, enabling superconductivity and revealing competing orders in La(O₁₋ₓFₓ)FeAs.

Abstract

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$_c$= 26 K in Fe-based oxypnictide La(O$_{1-x}$F$_x$)FeAs is a surprise to the scientific community\cite{Kamihara08}. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150 K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that the anomaly is caused by the spin-density-wave (SDW) instability, and electron-doping by F suppresses the SDW instability and recovers the superconductivity. Therefore, the La(O$_{1-x}$F$_x$)FeAs offers an exciting new system showing competing orders in layered compounds.