LaFeAsO$_{1-x}M_x$（$M={\rm F,H}$）第二超导穹顶中混合态线宽的异常场演化
Anomalous field evolution of the mixed-state linewidth in the second superconducting dome of LaFeAsO$_{1-x}M_x$ ($M={\rm F,H}$)
AI总结：
通过横向场μ子自旋旋转/弛豫研究LaFeAsO$_{1-x}M_x$混合态内场分布，发现低于$T_{\rm c}$时线宽增加，高于$T_{\rm c}$时与场有关。减去正常态贡献后，SC1和SC2样品超导线宽场依赖性不同，SC2有异常场演化，揭示了两超导穹顶不同电子特性。
AI中文摘要：
我们报告了对LaFeAsO$_{0.89}$F$_{0.11}$和LaFeAsO$_{0.75}$H$_{0.25}$混合态内场分布的横向场μ子自旋旋转/弛豫（$\mu$SR）研究，它们分别代表LaFeAsO$_{1-x}M_x$（$M={\rm F,H}$）家族的第一（SC1）和第二（SC2）超导穹顶。低于超导转变温度$T_{\rm c}$时，两个样品的内场分布线宽均增加，表明形成了涡旋晶格。高于$T_{\rm c}$时，线宽仍与场有关且随场近似线性增加。减去正常态贡献后，两个样品的超导线宽$\sigma_{\rm sc}$呈现出定性不同的场依赖性。4K时，SC1（$x_{\rm F}=0.11$）样品随场增加呈预期的单调下降，而SC2（$x_{\rm H}=0.25$）样品在3T附近出现明显的局部最大值。$\sigma_{\rm sc}(T,H)$的等高线表示进一步揭示了局部最大值的脊，其场位置$H_{\sigma,\max}(T)$随升温向低场移动并在$T_{\rm c}$附近消失。SC2样品中观察到的异常场演化与增强的泡利顺磁效应相关的额外场致贡献一致，突出了两个超导穹顶不同的电子特性。
英文摘要：
We report a transverse-field muon-spin rotation/relaxation ($μ$SR) study of the internal-field distribution in the mixed state of LaFeAsO$_{0.89}$F$_{0.11}$ and LaFeAsO$_{0.75}$H$_{0.25}$, representative of the first (SC1) and second (SC2) superconducting domes of the LaFeAsO$_{1-x}M_x$ ($M={\rm F,H}$) family, respectively. Below the superconducting transition temperature $T_{\rm c}$, the linewidth of the internal-field distribution increases in both samples, indicating the formation of a vortex lattice. Above $T_{\rm c}$, the linewidth remains field dependent and increases approximately linearly with field, consistent with broadening of the powder spectrum caused by an anisotropic Knight shift. After subtraction of this normal-state contribution, the superconducting linewidth $σ_{\rm sc}$ exhibits qualitatively different field dependences in the two samples. At 4K, the SC1 ($x_{\rm F}=0.11$) sample shows the expected monotonic decrease with increasing field, whereas the SC2 ($x_{\rm H}=0.25$) sample develops a pronounced local maximum near 3T. A contour representation of $σ_{\rm sc}(T,H)$ further reveals a ridge of local maxima whose field position, $H_{σ,\max}(T)$, shifts to lower fields upon warming and disappears near $T_{\rm c}$. The anomalous field evolution observed in the SC2 sample is consistent with an additional field-induced contribution associated with enhanced Pauli-paramagnetic effects, highlighting the distinct electronic character of the two superconducting domes.
