二维铁磁体在不同相互作用区域的线性响应
Linear response across interaction regimes in two-dimensional ferromagnets
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中文总结 AI 辅助
本文提出基于高斯和表示分布函数的方法求解线性化量子玻尔兹曼方程，明确二维铁磁体从弹道区到流体动力学区的温度驱动转变，其结果与单层CrCl₃的氮空位中心退相实验吻合，建立了通用的线性响应计算框架。
中文摘要 AI 辅助
二维铁磁体的最新发现激发了人们对理解和控制其自旋输运性质的浓厚兴趣。这些系统的一个核心微观特征是，由交换作用驱动的磁子-磁子相互作用具有强烈的动量依赖性：低动量磁子相互作用较弱，而高动量磁子则会发生强散射并表现出集体流体动力学行为。因此，要理解这类系统中的输运过程，需要一种能够同等描述弹道区和流体动力学区的微观描述方法。合适的框架是量子玻尔兹曼方程（QBE），但其求解因多维碰撞积分而极具挑战性。本文中，我们开发了一种基于将分布函数高效表示为高斯和的方法，该方法可使碰撞积分易于处理。此方法能够精确求解线性化QBE，并在宽温度和磁场范围内计算二维铁磁体的动量与频率分辨线性响应。特别地，我们明确了由温度驱动的转变：从以弱相互作用低动量磁子为主的弹道区，过渡到由强相互作用高动量模式主导的集体流体动力学区。将该方法应用于单层CrCl₃，我们获得了与近期氮空位中心退相实验的良好一致性，该实验报道了与磁子声一致的反常磁噪声。更广泛地说，我们的工作为在量子玻尔兹曼动力学框架下可描述的相互作用二维量子系统中，计算动量与频率分辨线性响应建立了通用框架。
英文摘要
Recent discoveries of two-dimensional (2D) ferromagnets have stimulated intense interest in understanding and controlling their spin transport properties. A central microscopic feature of these systems is that exchange-driven magnon--magnon interactions are strongly momentum dependent: low-momentum magnons interact weakly, while high-momentum ones can scatter strongly and exhibit collective hydrodynamic behavior. Understanding transport in such systems therefore requires a microscopic description capable of capturing ballistic and hydrodynamic regimes on equal footing. The natural framework is the quantum Boltzmann equation (QBE), whose solution is notoriously difficult because of the multidimensional collision integrals. Here, we develop a method based on an efficient representation of distribution functions as sums of Gaussians, which renders the collision integrals tractable. This approach enables accurate solution of the linearized QBE and computation of momentum- and frequency-resolved linear response in 2D ferromagnets across a broad range of temperatures and magnetic fields. In particular, we resolve a temperature-driven crossover from a ballistic regime dominated by weakly interacting low-momentum magnons to a collective hydrodynamic regime governed by strongly interacting high-momentum modes. Applying this method to monolayer CrCl$_3$, we obtain good agreement with recent nitrogen-vacancy-center dephasing experiments that reported anomalous magnetic noise consistent with magnon sound. More broadly, our work establishes a general framework for computing momentum- and frequency-resolved linear response in interacting 2D quantum systems describable within quantum Boltzmann kinetics.
