Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA.
Department of Applied Physics, Northwestern Polytechnical University, Xian, 710072, China.
Nat Commun. 2018 Aug 7;9(1):3128. doi: 10.1038/s41467-018-05529-2.
Understanding the interplay between nematicity, magnetism and superconductivity is pivotal for elucidating the physics of iron-based superconductors. Here we use neutron scattering to probe magnetic and nematic orders throughout the phase diagram of NaFeNiAs, finding that while both static antiferromagnetic and nematic orders compete with superconductivity, the onset temperatures for these two orders remain well separated approaching the putative quantum critical points. We uncover local orthorhombic distortions that persist well above the tetragonal-to-orthorhombic structural transition temperature T in underdoped samples and extend well into the overdoped regime that exhibits neither magnetic nor structural phase transitions. These unexpected local orthorhombic distortions display Curie-Weiss temperature dependence and become suppressed below the superconducting transition temperature T, suggesting that they result from the large nematic susceptibility near optimal superconductivity. Our results account for observations of rotational symmetry breaking above T, and attest to the presence of significant nematic fluctuations near optimal superconductivity.
理解向列性、磁性和超导性之间的相互作用对于阐明铁基超导体的物理性质至关重要。在这里，我们使用中子散射来探测整个 NaFeNiAs 相图中的磁有序和向列有序，发现虽然静态反铁磁序和向列有序都与超导性竞争，但这两个有序的起始温度在接近假定的量子临界点时仍然很好地分开。我们揭示了在欠掺杂样品中，在四方-正交结构转变温度 T 以上仍然存在的局部正交畸变，并且在没有磁相或结构相变的过掺杂区域中延伸得很好。这些出乎意料的局部正交畸变表现出居里-外斯温度依赖性，并在超导转变温度 T 以下被抑制，表明它们是由最优超导性附近的大向列各向异性敏感性引起的。我们的结果解释了 T 以上旋转对称性破坏的观察结果，并证明了在最优超导性附近存在显著的向列涨落。
