Abstract

We discuss collisionless kinetic equations describing the non-equilibrium dynamics of magnons in a ferromagnet exposed to an oscillating microwave field. Previously, this problem has been treated within the so-called “S-theory” where the collision integral in the kinetic equation for the magnon distribution is either neglected or taken into account phenomenologically via an effective relaxation time. However, the possibility of magnon condensation has not been included in S-theory. Moreover, the momentum integrations appearing in the magnon self-energies are usually decoupled by retaining only the term where the loop momentum is equal to the external momentum. In this work we critically examine the accuracy of these approximations and develop the proper extensions of S-theory. We show that these extensions can significantly modify the time evolution of the magnon distribution.

Graphical abstract

中文翻译：

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参数泵浦磁振子的无碰撞动力学理论

摘要

我们讨论了无碰撞动力学方程，该方程描述了暴露于振荡微波场的铁磁体中磁振子的非平衡动力学。以前，这个问题已经在所谓的“ S理论”中得到了解决，在该理论中，通过有效的弛豫时间，现象学上忽略了或忽略了针对马农分布的动力学方程式中的碰撞积分。但是，磁振子凝聚的可能性尚未包含在S理论中。而且，出现在磁振子自能量中的动量积分通常通过仅保留环路动量等于外部动量的项来解耦。在这项工作中，我们严格地检查了这些近似的准确性，并发展了S理论的适当扩展。

图形概要