AI 中文总结
研究 Mn2Mo3O8 的磁与振动激发，结合实验与从头算识别光频声子，发现磁有序态太赫兹带的磁圆二色性在4T自旋翻转跃迁以上消失，未观测到E2声子预期分裂。
AI 中文摘要
我们通过温度依赖拉曼散射和磁光太赫兹时域透射光谱，研究了共线 altermagnet 候选材料 Mn2Mo3O8 的磁激发与振动激发。通过与准确捕获振动本征模本征频率的从头算（ab initio）计算对比，我们识别出所有光频声子，包括此前拉曼研究中未发现的最低能量 A1 和 E2 型拉曼模式。此外，我们对比了 Mn2Mo3O8 的顺磁相和磁有序相中光活性声子的选择规则，并分析了关于伪角动量守恒的拉曼选择规则。未观测到预期的简并顺磁 E2 光频声子在磁有序时分裂为具有圆偏振模式的证据，这可能是由于 Mn2+ 典型的弱自旋轨道耦合。相反，我们在磁有序态中观测到宽太赫兹激发带处存在强磁圆二色性，该带可能源于双磁振子激发，仅具有电偶极活性，且具有依赖磁场的双组分精细结构，其磁圆二色性在 4 T 的自旋翻转跃迁以上消失。
英文摘要
We investigated the magnetic and vibrational excitations in the collinear altermagnet candidate \ce{Mn2Mo3O8} by temperature dependent Raman scattering and magneto-optical THz time-domain transmission spectroscopy. By comparison to \textit{ab initio} calculations accurately capturing the eigenfrequencies of the vibrational eigenmodes, we identify all optical phonons, including the lowest-lying Raman modes of $A_1$ and $E_2$ type, which had remained elusive in a previous Raman study. Moreover, we compare the selection rules for optically active phonons in the paramagnetic and the magnetically ordered phases of \ce{Mn2Mo3O8} and analyze the Raman selection rules with respect to pseudo-angular momentum conservation. No evidence of the expected splitting of the degenerate paramagnetic $E_2$ optical phonons into modes with circular polarization upon magnetic ordering could be resolved, likely due to weak spin-orbit coupling typical for Mn$^{2+}$. In contrast, we observe strong magnetic circular dichroism at a broad THz excitation band, emerging in the magnetically ordered state. This band, potentially originating from two-magnon excitations, is only electric-dipole active and features a field-dependent two-component fine structure. Its magnetic circular dichroism vanishes above the spin-flop transition at 4~T.
