近日，香港大学的Tran Trung Luu及其研究小组与瑞士洛桑联邦理工学院的Hans Jakob Wörner以及德国明斯特大学的Tilmann Kuhn等人合作并取得一项新进展。经过不懈努力，他们利用高谐波光谱探测了晶格动力学。相关研究成果已于2024年6月10日在国际知名学术期刊《自然—光子学》上发表。
本文证明了利用高谐波光谱可以实时探测电子-声子、非谐波声子-声子耦合及其弛豫动力学。该技术是无本底的，在能量域内展现出极高的灵敏度。结合密度泛函微扰理论计算的光学变形势和绝对能量调制深度，该测量揭示了α-石英晶体中邻近氧原子在实际空间中的最大位移可达数十微米。
通过对声子调制的高谐波谱进行简单而稳健的Gabor时间窗口分析，研究人员成功观测到了高度非线性相互作用中通道分辨的四声子散射过程。这一研究不仅为相干声子及其散射动力学的精确测量开辟了新的领域，也为固体物理中的潜在从头计算基准提供了有力支持。
据悉，固体中相干晶格振动的探测通常是使用时间分辨瞬态光谱学进行的，这种方法只能获得相对振荡幅度。利用时间分辨X射线技术，可以提取绝对电子-声子耦合强度。然而，这种实验的复杂性使得它不可能在传统的实验室中进行。
附：英文原文
Title: High-harmonic spectroscopy probes lattice dynamics
Author: Zhang, Jicai, Wang, Ziwen, Lengers, Frank, Wigger, Daniel, Reiter, Doris E., Kuhn, Tilmann, Worner, Hans Jakob, Luu, Tran Trung
Issue&Volume: 2024-06-10
Abstract: The probing of coherent lattice vibrations in solids has conventionally been carried out using time-resolved transient optical spectroscopy, with which only the relative oscillation amplitude can be obtained. Using time-resolved X-ray techniques, absolute electron–phonon coupling strength could be extracted. However, the complexity of such an experiment renders it impossible to be carried out in conventional laboratories. Here we demonstrate that the electron–phonon, anharmonic phonon–phonon coupling and their relaxation dynamics can be probed in real time using high-harmonic spectroscopy. Our technique is background-free and has extreme sensitivity directly in the energy domain. In combination with the optical deformation potential calculated from density functional perturbation theory and the absolute energy modulation depth, our measurement reveals the maximum displacement of neighbouring oxygen atoms in α-quartz crystal to tens of picometres in real space. By employing a straightforward and robust time-windowed Gabor analysis for the phonon-modulated high-harmonic spectrum, we successfully observe channel-resolved four-phonon scattering processes in such highly nonlinear interactions. Our work opens a new realm for the accurate measurement of coherent phonons and their scattering dynamics, which allows for potential benchmarking ab initio calculations in solids.
DOI: 10.1038/s41566-024-01457-4
Source: https://www.nature.com/articles/s41566-024-01457-4