钇铁石榴石中磁振子的热化：非平衡泛函重整化群方法
Thermalization of magnons in yttrium-iron garnet: nonequilibrium functional renormalization group approach
摘要：
利用非平衡泛函重整化群（FRG）方法计算了与热声子池接触的磁振子气体动量分布的时间演化。作为FRG过程的截止，我们使用杂化参数Λ，引起声子的人工阻尼。在我们截断的FRG流方程的时间演化的磁振子分布是从一个速率方程，涉及截止依赖的非平衡自能，这反过来又满足FRG流方程取决于截止依赖的过渡率。我们的方法超越了玻恩碰撞近似，并考虑到声子上的磁振子的反馈。我们用我们的方法计算了一个准二维磁振子气体的热化后的磁性绝缘体钇铁石榴石高激发的初始状态已产生的外部微波场。我们得到了很好的协议与最近的实验。
英文摘要：
Using a nonequilibrium functional renormalization group (FRG) approach we calculate the time evolution of the momentum distribution of a magnon gas in contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a hybridization parameter Λ giving rise to an artificial damping of the phonons. Within our truncation of the FRG flow equations the time evolution of the magnon distribution is obtained from a rate equation involving cutoff-dependent nonequilibrium self-energies, which in turn satisfy FRG flow equations depending on cutoff-dependent transition rates. Our approach goes beyond the Born collision approximation and takes the feedback of the magnons on the phonons into account. We use our method to calculate the thermalization of a quasi two-dimensional magnon gas in the magnetic insulator yttrium-iron garnet after a highly excited initial state has been generated by an external microwave field. We obtain good agreement with recent experiments.
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