AI 中文总结
本研究利用中子Larmor衍射测量多种铁基超导体的d间距分布，发现类居里-外斯展宽行为并通过平均场模型解释其机制，为向列弹性响应提供了体相敏感的新探测方法。
AI 中文摘要
铁基超导体（FeSCs）中的电子向列性与正交应变呈双线性耦合，使得向列关联可在晶格响应中显现。本研究采用中子Larmor衍射（拉莫尔衍射）技术，测量了电子掺杂Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$、空穴掺杂Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$、FeSe以及Fe$_{1.07}$Te的相对$d$间距随温度变化的分布。在未刻意施加单轴应力的Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$晶体中，面内分布宽度$\boldsymbol{\rm \textit{ε}_{FWHM}}$（半高全宽应变）随温度在四方相区冷却时增大，可通过类居里-外斯形式进行唯象描述。拟合得到的特征尺度$T^*$随Co掺杂量增加而降低，其演化规律与通过弹性电阻推断的向列相图相似，尽管两类实验探测的是不同的响应函数。Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$和FeSe中观测到的相关展宽效应，支持将这一解释推广至电子掺杂BaFe$_2$As$_2$之外的体系。相比之下，无外加应力时Fe$_{1.07}$Te未表现出延伸的类居里-外斯行为区间，而单轴压力会引发强烈的各向异性展宽，其贡献可能来自场偏置晶格响应与非均匀加载两方面。一个包含双线性向列弹性耦合与空间变化的对称破缺应力的平均场模型，可通过重整化的正交柔量解释类居里-外斯展宽行为。因此，中子Larmor衍射提供了一种对体相敏感的向列相关晶格展宽探测手段，可作为电子与弹性测量的补充。
英文摘要
Electronic nematicity in iron-based superconductors (FeSCs) couples bilinearly to orthorhombic strain, allowing nematic correlations to appear in the lattice response. Here we use neutron Larmor diffraction to measure the temperature-dependent distribution of relative $d$ spacings in electron-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole-doped Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$, FeSe, and Fe$_{1.07}$Te. In Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ crystals without intentionally applied uniaxial stress, the in-plane distribution width, $\varepsilon_{\rm FWHM}$, increases on cooling in the tetragonal phase and can be described phenomenologically by a Curie--Weiss-like form. The fitted scale $T^*$ decreases with Co doping and evolves similarly to the nematic phase diagram inferred from elastoresistance, although the two experiments probe different response functions. Related broadening in Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$ and FeSe supports extending this interpretation beyond electron-doped BaFe$_2$As$_2$. By contrast, Fe$_{1.07}$Te shows no extended Curie--Weiss-like regime without applied stress, whereas uniaxial pressure produces a strongly anisotropic broadening that can contain contributions from both the field-biased lattice response and inhomogeneous loading. A mean-field model with bilinear nematoelastic coupling and spatially varying symmetry-breaking stress explains the Curie--Weiss-like broadening in terms of the renormalized orthorhombic compliance. Neutron Larmor diffraction therefore provides a bulk-sensitive probe of nematic-related lattice broadening that complements electronic and elastic measurements.
Comments9 pages, 4 figures
