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Magnetic order close to superconductivity in theiron-based layered LaO_(1-x)F_xFeAs systems

机译：在其基于层的LaO_（1-x）F_xFeAs系统中接近超导的磁阶

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Following the discovery of long-range antiferromagnetic order in the parent compounds of high-transition-temperature (high-T_c) copper oxides, 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 electron or hole 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 susceptibility. 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 superconductivity, 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 PAmm) to monoclinic (space group P112) at low temperatures, and then, at ～137K, develops long-range SDW-type antiferromagnetic order with a small moment but simple magnetic structure~9. Doping the system with fluorine suppresses both the magnetic order and the structural distortion in favour of superconductivity. Therefore, like high-T_c copper oxides, the superconducting regime in these iron-based materials occurs in close proximity to a long-range-ordered antiferromagnetic ground state.
机译：在高转变温度（high-T_c）铜氧化物的母体化合物中发现远距离反铁磁有序之后，人们努力了解磁性在移动的“电子”或“空穴”发生时超导中的作用。被掺入反铁磁性母体化合物中。新发现的稀土铁基氧化物体系ROFeAs（R，稀土金属）中的超导性也源于其非超导母体化合物的电子或空穴掺杂。母体材料LaOFeAs是金属的，但在电阻率和d.c方面都显示出接近150 K的异常。磁化率。尽管光导率和理论计算表明LaOFeAs表现出自旋密度波（SDW）不稳定性，该不稳定性可通过掺杂电子来诱导超导来抑制，但尚无直接证据表明SDW有序。在这里，我们报告中子散射实验，结果表明LaOFeAs在155 K以下经历了突然的结构变形，在低温下，其对称性从四边形（空间群PA / nmm）变为单斜晶（空间群P112 / n），然后在〜 137K，开发出矩矩小但结构简单的长距离SDW型反铁磁命令〜9。用氟掺杂该系统抑制了磁序和结构畸变，有利于超导。因此，像高T_c铜氧化物一样，这些铁基材料中的超导机制非常接近于远距离有序的反铁磁基态。

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