标题： 阻尼铁磁系统的有效场论 显示英文标题

标题： An effective field theory of damped ferromagnetic systems

摘要： 利用in-in形式论，我们将最近构造的磁弹有效场理论（EFT）arXiv:2112.13873 [hep-th]推广，用于描述铁磁系统在长波长下的阻尼动力学。 我们发现标准的Gilbert阻尼项自然地以最简单的守恒对称性的非保守贡献形式出现在in-in框架中。 该EFT很容易推广到各向异性和非均匀性的情况。 特别是，当由常值外部背景场打破各向同性时，我们发现经典的Landau-Lifshitz阻尼项出现。 这为区分最初从现象学上构建的两种类型的阻尼动力学提供了第一原理的解释。 此外，使用spurion方法，EFT框架可以以直接的方式纳入材料的固有各向异性。 对于具有非平凡自旋纹理等非均匀性的系统，我们发现，最低阶导数修正给出了凝聚态文献中发现的广义Gilbert阻尼方程。 这表明，EFT方法能够以系统的方式推导出更高阶导数修正的形式。 最后，利用磁弹EFT中推导的声子-磁子耦合，我们能够预测声学对阻尼方程的贡献的一般形式。 显示英文摘要

摘要： Using the in-in formalism, we generalize the recently constructed magnetoelastic EFT arXiv:2112.13873 [hep-th] to describe the damping dynamics of ferromagnetic systems at long wavelengths. We find that the standard Gilbert damping term naturally arises as the simplest leading-order symmetry-consistent non-conservative contribution within the in-in framework. The EFT is easily generalized to scenarios with anisotropy and inhomogeneity. In particular, we find the classic Landau-Lifshitz damping term emerges when isotropy is broken by a constant external background field. This provides a first principle explanation for distinguishing the two types of damping dynamics that were originally constructed phenomenologically. Furthermore, the EFT framework could also incorporate intrinsic anisotropy of the material in a straightforward way using the spurion method. For systems with inhomogeneity such as nontrivial spin textures, we find that the leading order derivative correction yields the generalized Gilbert damping equations that were found in condensed matter literature. This shows that the EFT approach enables us to derive the form of higher-derivative-order corrections in a systematic way. Lastly, using the phonon-magnon coupling deduced in the magnetoelastic EFT, we are able to make a prediction for the generic form of the phononic contribution to the damping equation.