Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems

TL;DR

This paper demonstrates that LaOFeAs exhibits a structural distortion and SDW-type antiferromagnetic order below 150 K, which are suppressed by fluorine doping to induce superconductivity, highlighting the interplay between magnetism and superconductivity.

Contribution

It provides direct neutron scattering evidence of structural distortion and antiferromagnetic order in LaOFeAs, linking these phenomena to superconductivity upon doping.

Findings

Structural distortion occurs below 150 K in LaOFeAs.

Long-range SDW antiferromagnetic order develops at ~134 K.

Fluorine doping suppresses magnetic order and structural distortion, enabling superconductivity.

Abstract

In high-transition temperature (high-Tc) copper oxides, it is generally believed that antiferromagnetism plays a fundamental role in the superconducting mechanism because superconductivity occurs when mobile electrons or holes are doped into the antiferromagnetic parent compounds. The recent discovery of superconductivity in the rare-earth (R) iron-based oxide systems [RO1-xFxFeAs] has generated enormous interest because these materials are the first noncopper oxide superconductors with Tc exceeding 50 K. The parent (nonsuperconducting) LaOFeAs material is metallic but shows anomalies near 150 K in both resistivity and dc magnetic susceptibility. While optical conductivity and theoretical calculations suggest that LaOFeAs exhibits a spin-density-wave (SDW) instability that is suppressed with doping electrons to form superconductivity, there has been no direct evidence of the SDW order. Here we use neutron scattering to demonstrate that LaOFeAs undergoes an abrupt structural distortion below ~150 K, changing the symmetry from tetragonal (space group P4/nmm) to monoclinic (space group P112/n) at low temperatures, and then followed with the development of long range SDW-type antiferromagnetic order at ~134 K with a small moment but simple magnetic structure. Doping the system with flourine suppresses both the magnetic order and structural distortion in favor of superconductivity. Therefore, much like high-Tc copper oxides, the superconducting regime in these Fe-based materials occurs in close proximity to a long-range ordered antiferromagnetic ground state. Since the discovery of long