标题： 2H-NbSe₂中电荷密度波序在转变过程中的空间关联 显示英文标题

标题： Spatial correlations of charge density wave order across the transition in 2H-NbSe2

摘要： 电荷密度波（CDWs）涉及振幅和相位自由度的耦合，但直接获取局部位相关联仍然具有实验挑战性。 在这里，我们报告了通过液氦冷却至20K实现的2H-NbSe2中CDWs有序性的低温四维扫描透射电子显微镜（4D-STEM）测量。通过以纳米级分辨率绘制CDWs超晶格强度的空间分布并分析其自相关性，我们提取了与CDWs有序参数局部位相相关的温度依赖性关联长度，且该关联长度独立于全局相位相干性。 我们的结果显示，在转变温度之上弱短程振幅关联持续存在，并在冷却过程中显著增长，在20K时达到约150nm。这些发现表明明显偏离平均场预期，并确立了4D-STEM作为探测量子材料中空间非均匀电子序的强大工具。 显示英文摘要

摘要： Charge density waves (CDWs) involve coupled amplitude and phase degrees of freedom, but direct access to local amplitude correlations remains experimentally challenging. Here, we report cryogenic four-dimensional scanning transmission electron microscopy (4D-STEM) measurements of CDW ordering in 2H-NbSe2, enabled by liquid helium-based cooling down to 20 K. By mapping the spatial distribution of CDW superlattice intensities at nanometer-scale resolution and analyzing their autocorrelations, we extract the temperature-dependent correlation length associated with the local amplitude of the CDW order parameter, independent of global phase coherence. Our results reveal that weak short-range amplitude correlations persist above the transition temperature, and grow significantly upon cooling, reaching approximately 150 nm at 20 K. These findings demonstrate clear deviations from mean-field expectations and establish 4D-STEM as a powerful tool for probing spatially inhomogeneous electronic order in quantum materials.