近日，美国加州大学欧文分校Pan, Xiaoqing团队开发出频率相关声子各向异性的原子尺度成像。相关论文于2025年9月17日发表在《自然》杂志上。

直接可视化各个声子模式下的振动各向异性对于理解材料中各种有趣的光学、热和弹性现象至关重要。尽管传统的光学和衍射技术一直致力于估计振动各向异性，但它们在提供详细信息所需的空间和能量分辨率方面存在不足。

研究组介绍了一种新的动量选择电子能量损失谱，它使频率和对称性相关的振动各向异性的元素分辨成像具有原子分辨率。振动各向异性表现为不同规范的正交原子位移，称为热椭球。使用中心对称钛酸锶作为模型系统，研究组观察到两种不同类型的氧振动具有不同的各向异性：低于60meV和超过60mev的延长。在非中心对称的钛酸钡中，该方法可以通过观察55meV，它源于晶体对称性的降低，也可能与铁电极化有关。

这些观测结果在数量上得到理论模型的支持，这证明了该方法的可靠性。测量的频率相关振动各向异性揭示了由声学和光学声子控制的介电和热行为。以前所未有的空间和能量分辨率在特定晶体位置可视化声子特征向量的能力为探索介电、光学、热和超导性质开辟了新的途径。

附：英文原文

Title: Atomic-scale imaging of frequency-dependent phonon anisotropy

Author: Yan, Xingxu, Zeiger, Paul M., Huang, Yifeng, Sun, Haoying, Li, Jie, Gadre, Chaitanya A., Yang, Hongbin, He, Ri, Aoki, Toshihiro, Zhong, Zhicheng, Nie, Yuefeng, Wu, Ruqian, Rusz, Jn, Pan, Xiaoqing

Issue&Volume: 2025-09-17

Abstract: Directly visualizing vibrational anisotropy in individual phonon modes is essential for understanding a wide range of intriguing optical, thermal and elastic phenomena in materials1,2,3,4,5. Although conventional optical and diffraction techniques have been used to estimate vibrational anisotropies, they fall short in achieving the spatial and energy resolution necessary to provide detailed information4,5,6,7. Here, we introduce a new form of momentum-selective electron energy-loss spectroscopy, which enables the element-resolved imaging of frequency- and symmetry-dependent vibrational anisotropies with atomic resolution. Vibrational anisotropies manifest in different norms of orthogonal atomic displacements, known as thermal ellipsoids. Using the centrosymmetric strontium titanate as a model system, we observed two distinct types of oxygen vibrations with contrasting anisotropies: oblate thermal ellipsoids below 60meV and prolate ones above 60meV. In non-centrosymmetric barium titanate, our approach can detect subtle distortions of the oxygen octahedra by observing the unexpected modulation of q-selective signals between apical and equatorial oxygen sites near 55meV, which originates from reduced crystal symmetry and may also be linked to ferroelectric polarization. These observations are quantitatively supported by theoretical modelling, which demonstrates the reliability of our approach. The measured frequency-dependent vibrational anisotropies shed new light on the dielectric and thermal behaviours governed by acoustic and optical phonons. The ability to visualize phonon eigenvectors at specific crystallographic sites with unprecedented spatial and energy resolution opens new avenues for exploring dielectric, optical, thermal and superconducting properties.

DOI: 10.1038/s41586-025-09511-z

Source: https://www.nature.com/articles/s41586-025-09511-z