EuTiO$_3$ 中自旋极化与驱动圆离子运动的解耦
Disentangling spin polarization from driven circular ionic motion in EuTiO$_3$
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中文总结 AI 辅助
本研究通过X射线实验直接测量EuTiO$_3$中圆THz驱动的离子运动与自旋极化，发现离子运动不产生可检测的自旋极化，XMCD上限与经典贡献相差多个数量级，解耦了动态多铁性中的磁信号。
中文摘要 AI 辅助
相干驱动的圆离子运动已被报道产生大的螺旋度依赖光学响应，该响应被归因于瞬态磁化。然而，这一现象（有时称为动态多铁性）的微观本质和大小仍存在激烈争论。在此，我们利用X射线直接研究了高场圆太赫兹（THz）驱动引起的离子环流与其对EuTiO$_3$自旋系统的影响之间的联系。该材料表现出与在相关非磁性材料中观察到的假定磁信号一致的光学响应。此外，Eu$^{2+}$离子的存在使得能够使用X射线磁圆二色性（XMCD）来测试瞬态自旋极化的产生。同时，超快X射线衍射（XRD）测量圆离子运动，从中我们确定机械角动量。我们发现来自XRD的经典离子贡献为$3\times10^{-8}~\mu_B$，以及来自XMCD在铕$M_5$和$L_2$边（分别探测Eu$^{2+}$的$4f$和$5d$壳层）的灵敏度的上限分别为$0.03~\mu_B$和$0.11~\mu_B$。这些观察表明，尽管光学数据中有清晰的特征，但该系统中大幅度的圆离子运动并未伴随可检测的自旋极化，XMCD上限与经典贡献相差多个数量级。
英文摘要
Coherently driven circular ionic motion has been reported to produce large helicity-dependent optical responses attributed to transient magnetization. However, the microscopic nature and magnitude of this phenomenon, sometimes referred to as dynamical multiferroicity, remain strongly debated. Here, we directly study the connection between ionic circulation induced by a high-field circular terahertz (THz) drive and its effect on the spin system of EuTiO$_3$ using X-rays. This material exhibits an optical response consistent with the putative magnetic signal observed in related non-magnetic materials. Furthermore, the presence of Eu$^{2+}$ ions enables the use of X-ray magnetic circular dichroism (XMCD) to test for the creation of transient spin polarization. Simultaneously, ultrafast X-ray diffraction (XRD) measures the circular ionic motion from which we determine the mechanical angular momentum. We find a classical ionic contribution of $3\times10^{-8}~μ_B$ from XRD and upper limits of $0.03~μ_B$ and $0.11~μ_B$ from the sensitivity of XMCD at the europium $M_5$ and $L_2$ edges, probing the $4f$ and $5d$ shells of Eu$^{2+}$, respectively. These observations show that large-amplitude circular ionic motion in this system is not accompanied by a detectable spin polarization despite the clear signature in the optical data, with the XMCD upper bounds and classical contribution differing by many orders of magnitude.
发表机构
- Paul Scherrer Institut（保罗谢勒研究所）
- Brigham Young University（杨百翰大学）
- ETH Zurich（苏黎世联邦理工学院）
- SLAC National Accelerator Laboratory, Stanford University（斯坦福大学SLAC国家加速器实验室）
机构由 AI 辅助整理，请以论文原文为准。
