Christopher Heins, Lukas Körber, Joo-Von Kim, Thibaut Devolder, Johan H. Mentink, Attila Kákay, Jürgen Fassbender, Katrin Schultheiss, Helmut Schultheiss
Driving condensed matter systems with periodic electromagnetic fields can result in exotic states not found in equilibrium. Termed Floquet engineering, such periodic driving applied to electronic systems can tailor quantum effects to induce topological band structures and control spin interactions. However, Floquet engineering of magnon band structures in magnetic systems has proven challenging so far. Here, we present a class of Floquet states in a magnetic vortex that arise from nonlinear interactions between the vortex core and microwave magnons. Floquet bands emerge through the periodic oscillation of the core, which can be initiated by either driving the core directly or pumping azimuthal magnon modes. For the latter, the azimuthal modes induce core gyration through nonlinear interactions, which in turn renormalizes the magnon band structure. This represents a self-induced mechanism for Floquet band engineering and offers new avenues to study and control nonlinear magnon dynamics.
Time-resolved observation of magnon splitting into vortex gyration and Floquet spin waves
Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies（巴黎萨克雷大学）；Helmholtz-Zentrum Dresden–Rossendorf（德累斯顿-罗森多夫亥姆霍兹中心）；International Iberian Nanotechnology Laboratory（伊比利亚纳米技术国际实验室）
International Quantum Academy（国际量子学院）；Beihang University（北京航空航天大学）；Universidad Técnica Federico Santa María（弗雷德里科·Santa María 技术大学）；Cnr-Istituto Officina dei Materiali（意大利国家研究委员会材料研究所）
Magnetic vortex dynamics in a 2D easy plane ferromagnet
在这篇论文中，我们考虑二维易平面绝缘铁磁体中的涡旋动力学。除了准粒子激发，这里自旋波或磁振子，这个磁系统承认家庭的涡旋解决方案进行两个拓扑不变量，绕组数或涡度，和极化。涡旋近似地被描述为围绕系统运动的粒子，被赋予有效质量并受到各种力的作用。在经典中，涡具有涡间势能，产生类似库仑力（吸引力或排斥力取决于相对涡度）和回转力，表现为自诱导洛伦兹力，其方向取决于两个拓扑指数。通过对多涡解进行半经典展开，考虑散射磁振子态，对涡旋进行量子化，给出零点能量修正和多涡质量张量。涡不能被描述为独立的粒子-也就是说，有非对角质量项，如1/2 Mij vi vj，这是不可忽略的。本论文通过计算Feynman-Vernon影响泛函来进一步详细研究整个涡旋动力学，Feynman-Vernon影响泛函描述了在磁振子模被追踪之后涡旋密度矩阵的演化。除了已知的一组力，我们发现新的阻尼力作用在纵向和横向的旋涡运动。在一个集体中的旋涡运动不能完全分开：由于一个旋涡的运动，另一个旋涡受到阻尼力的作用。有效阻尼力具有记忆效应：它们不仅取决于涡流集合的当前运动，而且还取决于运动历史。
