发表机构
Beijing Academy of Quantum Information Sciences; Rutgers University; Keck Center for Quantum Magnetism, Rutgers University; National Institute of Chemical Physics and Biophysics（北京量子信息科学研究院; 罗格斯大学; 罗格斯大学凯克量子磁学中心; 化学物理与生物物理学国立研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用偏振分辨拉曼光谱在Cr$_2$O$_3$中首次直接观测到具有反对称拉曼张量的$A_2$声子模式，该模式携带固有声子角动量，其频率和椭圆运动与第一性原理计算吻合，为探测对称禁戒声子模式提供新途径。
AI 中文摘要
声子角动量以原子的圆周或椭圆运动为特征，在多种现象中起决定性作用，包括声子霍尔效应、声子磁矩、爱因斯坦-德哈斯效应、外尔声子和驱动手性声子。具有反对称拉曼张量的声子模式在赝矢量对称通道中携带固有声子角动量，但过去在手性声子领域中被忽视。在此，我们报告利用偏振分辨拉曼光谱检测此类声子模式。我们在Cr$_2$O$_3$的反铁磁手性相的$A_2$-赝矢量对称通道中观测到266cm$^{-1}$处的声子。该$A_2$模式的频率和椭圆运动被第一性原理声子计算捕获，该计算将晶格和自旋平等地视为“慢”自由度。由于Cr$_2$O$_3$中存在Cr空位，局部破坏了垂直于三重轴的二重旋转对称性，该模式获得拉曼活性。我们的结果为检测赝矢量对称通道中具有反对称拉曼张量的新型对称禁戒$A_2$声子模式提供了新方法。
英文摘要
Phonon angular momentum, characterized by circular or elliptical motion of atoms, plays a decisive role in diverse phenomena, ranging from the phonon Hall effect, phonon magnetic moment, Einstein-de Haas effect, Weyl phonons, and driven chiral phonons. The phonon modes with an antisymmetric Raman tensor, which carry an intrinsic phonon angular momentum in a pseudovector symmetry channel, have been overlooked in the past in the chiral phonon community. Here, we report the detection of this type of phonon mode using polarization-resolved Raman spectroscopy. We observe a phonon at 266cm$^{-1}$ in the antiferromagnetic chiral phase of Cr$_2$O$_3$ in the $A_2$-pseudovector symmetry channel. This $A_2$ mode's frequency and the elliptical motion are captured by first-principles phonon calculations, which treat both lattice and spins on an equal footing as 'slow' degrees of freedom. This mode gets Raman activity due to the presence of Cr vacancies in Cr$_2$O$_3$ that locally break the twofold rotational symmetry perpendicular to the threefold axis. Our results provide a new way to detect the novel symmetry-forbidden $A_2$ phonon modes with an antisymmetric Raman tensor in a pseudovector symmetry channel.
Comments25 pages, 4 figures
