【摘要】 原子级薄的范德华磁性材料不仅为探索二维极限下的基本物理学提供了肥沃的土壤,也为新型超快功能器件创造了巨大的机会.本文系统研究了少层拓扑反铁磁MnBi₂Te₄晶体在不同层厚、温度和磁场下的超快磁化率和自旋波动力学.作者发现激光诱导的（退）磁化过程可用于精确地跟踪不同磁场区域中的不同磁状态,包括显示出明显的奇偶层数效应.此外,频率为数十千兆赫兹的反铁磁磁振子模式可以被光脉冲激发并在时域中直接被观察到,其频率强烈地依赖于磁场.值得注意的是,磁化率和磁振子动力学不仅可以在时间分辨的磁光克尔效应中观察到,而且在时间分辨的反射率中也可以观察到,这表明磁态和电子结构之间存在很强的相关性.本工作研究了这种新型二维反铁磁体中的超快自旋动力学,为二维反铁磁自旋电子学和磁振子学的潜在应用以及磁态和拓扑量子态的超快调控研究铺平了道路.更多还原

【Abstract】 Atomically thin van der Waals magnetic materials have not only provided a fertile playground to explore basic physics in the two-dimensional（2D） limit but also created vast opportunities for novel ultrafast functional devices. Here we systematically investigate ultrafast magnetization dynamics and spin wave dynamics in few-layer topological antiferromagnetic MnBi₂Te₄ crystals as a function of layer number,temperature, and magnetic field. We find laser-induced（de）magnetization processes can be used to accurately track the distinct magnetic states in different magnetic field regimes, including showing clear odd-even layer number effects. In addition, strongly field-dependent AFM magnon modes with tens of gigahertz frequencies are optically generated and directly observed in the time domain. Remarkably, we find that magnetization and magnon dynamics can be observed in not only the time-resolved magnetooptical Kerr effect but also the time resolved reflectivity, indicating strong correlation between the magnetic state and electronic structure. These measurements present the first comprehensive overview of ultrafast spin dynamics in this novel 2D antiferromagnet, paving the way for potential applications in 2D antiferromagnetic spintronics and magnonics as well as further studies of ultrafast control of both magnetization and topological quantum states.更多还原