标题： 将光引入兰道-利夫希茨-吉尔伯特方程：其分数非马尔可夫记忆核对光学诱导的磁惯性和磁振子的影响 显示英文标题

标题： Bringing light into the Landau-Lifshitz-Gilbert equation: Consequences of its fractal non-Markovian memory kernel for optically induced magnetic inertia and magnons

摘要： 朗道-利斯季格-吉尔伯特（LLG）方程一直是建模非平衡磁体中被视为固定长度的经典矢量的定域自旋动力学的核心。当光作为非平衡驱动时，LLG 方程必须补充一些额外项，这些项通常通过经典的直接自旋-轨道耦合现象学论证来推测，以描述定域自旋与光的真实或有效磁场之间的直接耦合。 然而，磁场与自旋的直接耦合比光与电子的耦合小一个光速因子；或者磁场和电场的变化太快，慢的经典自旋无法跟上。在这里，我们通过施温格-凯尔迪什场论（SKFT）严格推导出扩展的 LLG 方程，从而避免了经典现象学论证的需求。 在这样的理论中，光与迁移电子相互作用，然后由它们携带的自旋流对定域自旋施加自旋转移转矩，因此当光激发电子被积分后，我们得到一个仅涉及自旋的方程。与具有局部时间 Gilbert 阻尼的标准现象学 LLG 方程不同，我们的扩展方程包含一个非马尔可夫记忆核，在其两个时间变量的平面图中表现出分形性质。 通过将基于 SKFT 推导出的扩展 LLG 方程作为我们的中心结果应用于光驱动铁磁体为例，我们预测了一个光学诱导的磁惯性项。其大小由空间非局域且时间相关的前因子控制，导致在相干（或热）声子带内和带外的尖锐频率处激发相干声子。 显示英文摘要

摘要： The Landau-Lisfhitz-Gilbert (LLG) equation has been the cornerstone of modeling the dynamics of localized spins, viewed as classical vectors of fixed length, within nonequilibrium magnets. When light is employed as the nonequilibrium drive, the LLG equation must be supplemented with additional terms that are usually conjectured using phenomenological arguments for direct opto-magnetic coupling between localized spins and (real or effective) magnetic field of light. However, direct coupling of magnetic field to spins is 1/c smaller than coupling of light and electrons; or both magnetic and electric fields are too fast for slow classical spins to be able to follow them. Here, we displace the need for phenomenological arguments by rigorously deriving an extended LLG equation via Schwinger-Keldysh field theory (SKFT). Within such a theory, light interacts with itinerant electrons, and then spin current carried by them exerts spin-transfer torque onto localized spins, so that when photoexcited electrons are integrated out we arrive at a spin-only equation. Unlike the standard phenomenological LLG equation with local-in-time Gilbert damping, our extended one contains a non-Markovian memory kernel whose plot within the plane of its two times variables exhibits fractal properties. By applying SKFT-derived extended LLG equation, as our central result, to a light-driven ferromagnet as an example, we predict an optically induced magnetic inertia term. Its magnitude is governed by spatially nonlocal and time-dependent prefactor, leading to excitation of coherent magnons at sharp frequencies in and outside of the band of incoherent (or thermal) magnons.