Cr$_2$O$_3$磁电张量的频率依赖自旋贡献：一项第一性原理研究
The Frequency-Dependent Spin Contribution to the Magnetoelectric Tensor of Cr$_2$O$_3$: A First-Principles Study
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中文总结 AI 辅助
本文采用第一性原理研究Cr$_2$O$_3$的频率依赖自旋诱导线性ME响应，对比IPA、RPA、TDDFT、BSE四种方法，发现BSE可复现激子共振，TDDFT能给出类磁振子峰及可观静态响应，揭示不同方法对动力学ME响应的互补捕捉作用。
中文摘要 AI 辅助
磁电（ME）效应为利用电场调控磁性功能提供了极具前景的途径。尽管静态线性ME响应的第一性原理方法已相当成熟，但实验表明存在显著的有限频率共振，而频率依赖响应的可比方法仍发展不足。本文从第一性原理出发研究动力学自旋诱导线性ME响应，系统对比了独立粒子近似（IPA）、随机相位近似（RPA）、含时密度泛函理论（TDDFT）以及Bethe-Salpeter方程（BSE）这四种方法。我们将这些方法应用于典型ME材料Cr$_2$O$_3$，并与现有实验及理论研究结果进行对比。研究发现，IPA和RPA无法复现先前报道的自旋诱导响应的有限静态极限。在BSE框架内，ME光谱中出现了显著的激子共振，与实验结果定性一致。我们还识别出一个类磁振子峰，其与横向自旋磁化率的极点重合，但在光吸收中基本呈暗态，凸显了ME响应对自旋激发的敏感性。TDDFT将该模式置于预期的低能磁振子区域附近，并产生可观的静态自旋诱导响应。我们的结果表明，这些框架捕捉了动力学ME响应的互补方面：要复现静态极限需要低能集体自旋激发，而电子-空穴相互作用对复现激子共振至关重要。
英文摘要
The magnetoelectric (ME) effect provides a promising pathway for controlling magnetic functionalities using electric fields. While first-principles methods for the static linear ME response are well established, comparable approaches for the frequency-dependent response remain less developed, despite experiments showing pronounced finite-frequency resonances. Here, we investigate the dynamical spin-induced linear ME response from first principles and systematically compare the independent-particle approximation (IPA), random-phase approximation (RPA), time-dependent density functional theory (TDDFT), and the Bethe-Salpeter equation (BSE). We apply these methods to the prototypical ME material Cr$_2$O$_3$ and compare the results with available experimental and theoretical studies. We find that the IPA and RPA fail to reproduce the previously reported finite static limit of the spin-induced response. Within the BSE framework, pronounced excitonic resonances emerge in the ME spectrum, in qualitative agreement with experiment. We also identify a magnon-like peak that coincides with a pole of the transverse spin susceptibility while remaining essentially dark in optical absorption, highlighting the sensitivity of the ME response to spin excitations. TDDFT places this mode closer to the expected low-energy magnonic regime and yields a sizable static spin-induced response. Our results show that these frameworks capture complementary aspects of the dynamical ME response. Low-energy collective spin excitations are required to recover the static limit, whereas electron-hole interactions are essential for reproducing the excitonic resonances.
