通过逆法拉第效应解析SrTiO$_3$中瞬态自旋和轨道磁化动力学
Disentangling the dynamics of transient spin and orbital magnetization in SrTiO$_3$ via the inverse Faraday effect from RT-TDDFT
AI总结：
通过逆法拉第效应研究SrTiO$_3$中瞬态自旋和轨道磁化动力学，揭示光角动量转移主导电子轨道角动量，自旋轨道耦合起关键作用。
摘要：
光物质相互作用使得非平衡态得以实现，这些态在其他情况下是无法达到的。受最近实验报告的影响，这些实验在典型的反铁磁带绝缘体SrTiO$_3$中报告了铁电性，甚至多铁性，这是通过太赫兹脉冲诱导的。我们研究了由线性和圆极化光激发的SrTiO$_3$中的载流子和磁化动力学。我们的实时时间依赖密度泛函理论（RT-TDDFT）结果揭示了高度非平凡的、位点和轨道依赖的时间演变，其中电荷从O $2p$态转移到Ti $3d$态。对于线性极化光，电子密度在氧和钛位点的轨道极化笼子出现相位差波动，类似于软横纵光学声子模式，动态破坏反演对称性。相比之下，圆极化脉冲诱导了围绕O的电荷偶极子的相干旋转。这诱导了具有相反符号的瞬态磁化，即使没有离子运动。详细分析揭示，主导机制是将光的角动量转移到电子轨道角动量，而自旋轨道耦合在轨道到自旋角动量的转移中起关键作用，前者比后者大一个数量级。
英文摘要：
Motivated by recent evidence of ferroelectricity and even multiferroicity in the prototypical diamagnetic band insulator SrTiO$_3$ from terahertz experiments, we investigate the carrier and magnetization dynamics of SrTiO$_3$ excited optically by linearly (LPL) and circularly polarized light (CPL). Our RT-TDDFT simulations show a pronounced site- and orbital-dependent charge transfer from O$2p$ to Ti $3d$ states. With LPL anti-phase oscillations of the electron-density lobes at O and Ti resemble the soft transverse optical phonon mode and break dynamically inversion symmetry. CPL instead drives a coherent rotation of the charge dipoles around oxygen, producing a helicity-dependent transient magnetization of opposite sign at O and Ti, even without ionic motion. The dominant effect stems from the transfer of angular momentum (AM) from light to the electronic orbital AM, while spin-orbit coupling plays a key role in the transfer from orbital to spin AM, the former being an order of magnitude larger than the latter. The real-time resolution allows us to disentangle the inverse Faraday effect, which follows the pulse envelope, from optical orientation, which builds up during the pulse and saturates afterwards. The results demonstrate that purely electronic processes without lattice motion induce ultrafast magnetisation in a non magnetic insulator, offering a tunable route for light controlled magnetic functionalities.
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