Na Woongki, Park Pyeongjae, Oh Siwon, Kim Junghyun, Scheie Allen, Tennant David Alan, Lee Hyun Cheol, Park Je-Geun, Cheong Hyeonsik
Department of Physics, Sogang University, Seoul 04107, Korea.
Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea.
ACS Nano. 2024 Jul 29. doi: 10.1021/acsnano.4c04824.
van der Waals (vdW) magnets have rapidly emerged as a fertile playground for fundamental physics and exciting applications. Despite the impressive developments over the past few years, technical limitations pose a severe challenge to many other potential breakthroughs. High on the list is the lack of suitable experimental tools for studying spin dynamics on atomically thin samples. Here, Raman scattering techniques are employed to directly observe the low-lying magnon (∼1 meV) even in bilayer NiPS. The advantage is that it offers excellent energy resolutions far better on low-energy sides than most inelastic neutron spectrometers can offer. More importantly, with appropriate theoretical analysis, the polarization dependence of the Raman scattering by those low-lying magnons also provides otherwise hidden information on the dominant spin-exchange scattering paths for different magnons. By comparing with high-resolution inelastic neutron scattering data, these low-energy Raman modes are confirmed to be indeed of magnon origin. Because of the different scattering mechanisms involved in inelastic neutron and Raman scattering, this information is fundamental in pinning down the final spin Hamiltonian. This work demonstrates the capability of Raman spectroscopy to probe the genuine two-dimensional spin dynamics in atomically thin vdW magnets, which can provide insights that are obscured in bulk spin dynamics.
范德瓦尔斯（vdW）磁体迅速成为基础物理学和令人兴奋的应用的肥沃试验场。尽管在过去几年中取得了令人瞩目的进展，但技术限制对许多其他潜在突破构成了严峻挑战。其中最突出的是缺乏用于研究原子级薄样品上自旋动力学的合适实验工具。在此，拉曼散射技术被用于直接观测即使在双层NiPS中的低能磁振子（~1毫电子伏特）。其优势在于，它在低能侧提供了比大多数非弹性中子谱仪更好的出色能量分辨率。更重要的是，通过适当的理论分析，这些低能磁振子的拉曼散射的偏振依赖性还提供了关于不同磁振子的主要自旋交换散射路径的隐藏信息。通过与高分辨率非弹性中子散射数据进行比较，这些低能拉曼模式被证实确实源自磁振子。由于非弹性中子散射和拉曼散射涉及不同的散射机制，该信息对于确定最终的自旋哈密顿量至关重要。这项工作展示了拉曼光谱探测原子级薄vdW磁体中真正二维自旋动力学的能力，这可以提供在体自旋动力学中被掩盖的见解。
