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Magnetic order close to superconductivity in the iron-based layered LaO1-xF x FeAs systems

Abstract

Following the discovery of long-range antiferromagnetic order in the parent compounds of high-transition-temperature (high-Tc) copper oxides1,2, there have been efforts to understand the role of magnetism in the superconductivity that occurs when mobile ‘electrons’ or ‘holes’ are doped into the antiferromagnetic parent compounds. Superconductivity in the newly discovered rare-earth iron-based oxide systems ROFeAs (R, rare-earth metal) also arises from either electron3,4,5,6,7 or hole8 doping of their non-superconducting parent compounds. The parent material LaOFeAs is metallic but shows anomalies near 150 K in both resistivity and d.c. magnetic susceptibility3. Although optical conductivity and theoretical calculations suggest that LaOFeAs exhibits a spin-density-wave (SDW) instability that is suppressed by doping with electrons to induce superconductivity9, there has been no direct evidence of SDW order. Here we report neutron-scattering experiments that demonstrate that LaOFeAs undergoes an abrupt structural distortion below 155 K, changing the symmetry from tetragonal (space group P4/nmm) to monoclinic (space group P112/n) at low temperatures, and then, at 137 K, develops long-range SDW-type antiferromagnetic order with a small moment but simple magnetic structure9. Doping the system with fluorine suppresses both the magnetic order and the structural distortion in favour of superconductivity. Therefore, like high-Tc copper oxides, the superconducting regime in these iron-based materials occurs in close proximity to a long-range-ordered antiferromagnetic ground state.

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Figure 1: Temperature dependence of the nuclear structures for LaOFeAs and LaO 0.92 F 0.08 FeAs.
Figure 2: Temperature dependence of the (2, 2, 0) nuclear reflection indicative of a structural phase transition at 155 K in LaOFeAs.
Figure 3: Temperature dependence of the magnetic scattering for LaOFeAs and LaO 0.92 F 0.08 FeAs.
Figure 4: Temperature dependence of the order parameter at Q = 1.53 Å -1 , obtained using the magnetic structure we determine for LaOFeAs.

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Acknowledgements

We thank J. A. Fernandez-Baca, H. P. Cheng, T. Yildirim and C. Brown for discussions. This work is supported by the US Department of Energy, Division of Materials Science and Division of Scientific User Facilities, Basic Energy Sciences. This work is also supported by the US Department of Energy through UT/Battelle LLC. The work at the Institute of Physics, Chinese Academy of Sciences, is supported by the Natural Science Foundation of China, the Chinese Academy of Sciences and the Ministry of Science and Technology of China.

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Correspondence to Pengcheng Dai.

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de la Cruz, C., Huang, Q., Lynn, J. et al. Magnetic order close to superconductivity in the iron-based layered LaO1-xF x FeAs systems. Nature 453, 899–902 (2008). https://doi.org/10.1038/nature07057

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