量化相干驱动圆声子的角动量
Quantifying angular momentum of coherently driven circular phonons
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中文总结 AI 辅助
利用超快X射线衍射测量太赫兹圆偏振光驱动的SrTiO3中离子轨迹，发现氧离子贡献约90%的声子角动量，解释了诱导磁性的机制，并首次定量测量了圆离子运动及其角动量。
中文摘要 AI 辅助
利用强太赫兹脉冲操纵低能激发为超快控制材料电子和磁性质提供了强大方法。理论表明，太赫兹场驱动的圆离子运动携带角动量，可能产生内磁场。最近在非磁性SrTiO3中的实验暗示了这种太赫兹诱导场，但其起源仍有争议。这里，我们采用超快X射线衍射解析圆偏振太赫兹脉冲激发后SrTiO3中随时间变化的离子轨迹。我们的分析显示，氧离子尽管质量较低，却贡献了约90%的声子角动量。负电荷与正电荷离子之间的不平衡为SrTiO3中诱导磁性的机制提供了清晰解释。这项工作进一步提供了圆离子运动及其角动量的首次定量测量，并建立了研究固体中角动量转移的通用方法，为控制量子材料中拓扑声子输运和声子驱动磁性铺平了道路。
英文摘要
The use of intense terahertz (THz) pulses to manipulate low-energy excitations offers a powerful approach for ultrafast control of electronic and magnetic properties in materials. Theory suggests that circular ionic motions driven by THz fields carry angular momentum, potentially generating internal magnetic fields. Recent experiments in nonmagnetic SrTiO3 (STO) have hinted at such THz-induced fields, but their origin remains debated. Here, we employ ultrafast x-ray diffraction to resolve the time-dependent ionic trajectories in STO following excitation by circularly polarized THz pulses. Our analysis reveals that oxygen ions, despite their lower mass, contribute around 90% of the phonon angular momentum. The resulting imbalance between the negatively and positively charged ions provides a clear explanation for the mechanism behind induced magnetism in STO. This work further provides the first quantitative measurement of circular ionic motions and their angular momentum and establishes a general methodology for the investigation of angular momentum transfer in solids, paving the way for new strategies to control topological phonon transport and phonon-driven magnetism in quantum materials.
