Ranhili Jayajeewana N, Khadka Sumit, Li Junjie, Cenker John, Ruiz Alberto M, Shumilin Andrei, Baldoví José J, Shen Ka, Fedurin Mikhail, Palmer Mark, Chica Daniel G, Byaruhanga Paul, Chen Shuo, Xu Xiaodong, Roy Xavier, Freelon Byron
Physics Department and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA.
Accelerator Test Facility, Brookhaven National Laboratory, Upton, New York 11973, USA.
Struct Dyn. 2025 Mar 20;12(2):024501. doi: 10.1063/4.0000266. eCollection 2025 Mar.
Magnetism in two-dimensional (2D) van der Waals (vdW) crystals offers promising new directions for low-dimensional physics and devices. In this work, mega-electron volt (MeV) ultrafast electron diffraction was employed to investigate the ultrafast atomic dynamics of a novel, 2D vdW magnetic single-crystal CrSBr. Femtosecond (fs) optical pump pulses excited non-equilibrium atomic displacements shown to be coherent acoustic phonons (CAPs). Phonon frequencies were extracted by analyzing oscillations of different Bragg peak (BP) intensities and were determined to be GHz acoustic disturbances that propagated as strain waves. Phonon modes exhibit anisotropy with respect to the and crystal axes. Subharmonic phonon frequencies were also observed, and this provided a signature of nonlinear oscillatory coupling between the laser-induced pumping phonon frequency and secondary phonon frequencies. Thus, CrSBr was found to serve as a nonlinear phononic frequency converter. The ultrafast time dependence of the Bragg intensity was simulated by incorporating an oscillating deviation parameter into expressions for the dynamical scattering intensity yielded excellent modeling of the ultrafast structural dynamics of the photo-excited 2D crystal. Our work provides a foundation for exploring how fs light pulses can influence phonon dynamics in materials with strong spin-lattice coupling. These results suggest that CAPs can match the magnon frequencies and show the promise of CrSBr for use in optical-to-microwave transducers and phononic devices.
二维（2D）范德华（vdW）晶体中的磁性为低维物理和器件提供了充满前景的新方向。在这项工作中，利用兆电子伏特（MeV）超快电子衍射研究了一种新型二维vdW磁性单晶CrSBr的超快原子动力学。飞秒（fs）光泵浦脉冲激发的非平衡原子位移表现为相干声子（CAPs）。通过分析不同布拉格峰（BP）强度的振荡来提取声子频率，确定其为以应变波形式传播的吉赫兹声学扰动。声子模式相对于晶体轴呈现各向异性。还观察到了亚谐波声子频率，这为激光诱导泵浦声子频率与二次声子频率之间的非线性振荡耦合提供了一个特征。因此，发现CrSBr可作为非线性声子频率转换器。通过将振荡偏差参数纳入动态散射强度表达式，模拟了布拉格强度的超快时间依赖性，对光激发二维晶体的超快结构动力学进行了出色的建模。我们的工作为探索飞秒光脉冲如何影响具有强自旋 - 晶格耦合的材料中的声子动力学奠定了基础。这些结果表明，相干声子可以与磁振子频率匹配，并显示出CrSBr在光 - 微波换能器和声子器件中的应用前景。
