铁磁绝缘体中磁振子的非平衡稳态输运性质
Nonequilibrium steady-state transport properties of magnons in ferromagnetic insulators
杨栋超 1易立志 1丁林杰 2刘敏 1朱丽娅 1许云丽 1何雄 1沈顺清 3潘礼庆 1John Q.Xiao4
作者信息
- 1. 三峡大学理学院,湖北省弱磁探测工程技术研究中心,宜昌 443002
- 2. 三峡学院物理系,重庆 404100
- 3. 香港大学物理系,香港 999077
- 4. Department of Physics and Astronomy,University of Delaware,Newark 19716,USA
- 折叠
摘要
玻色子体系中的非平衡输运过程研究是极具挑战性的工作.磁振子是玻色子,具有与电子等费米子截然不同的自旋输运行为.本文以钇铁石榴石(YIG)铁磁绝缘体为研究对象,聚焦影响稳态下YIG中磁振子非平衡输运过程的关键因素.通过将具有非零化学势μm的玻色-爱因斯坦统计函数引入到玻尔兹曼输运方程中,获得了以α为幂次的输运方程严格解析表达式(当α(=-μm/(kBT))＜1时).结果显示,当α(＜＜)1时,我们得到了与以往研究不同的化学势μm与非平衡粒子浓度δnm之间的非线性关系δnm ∝-α1/2 ∝-(-μm)1/2;α较大时,则还须考虑其高阶项.正因这种非线性关系,导致磁振子扩散方程显著不同于电子自旋扩散特性,其由线性微分方程演变为更复杂的非线性微分方程.本文重点研究了在两种极端温度梯度(即▽T～1 K/mm和104 K/mm)下非平衡磁振子浓度δnm和化学势μm的空间分布,它们分别对应于μm的值约为-0.1 μeV和-6.2 meV,均满足前提条件α＜1.在远离平衡态的大温度梯度分布下,本文理论计算与实验结果吻合很好.这些理论研究结果将加深人们对铁磁绝缘体中磁振子非平衡输运行为的认识.
Abstract
Understanding nonequilibrium transport phenomena in bosonic systems is highly challenging.Magnons,as bosons,exhibit different transport behavior from fermionic electron spins.This study focuses on the key factors influencing the nonequilibrium transport of magnons in steady states within magnetic insulators by taking Y3Fe5O12(YIG)for example.By incorporating the Bose-Einstein distribution function with a non-zero chemical potential μm into the Boltzmann transport equation,analytical expressions for transport parameters in power of a(=-μm/(kBT))are obtained under the condition α＜1.It is the biggest different from previous researches that our theory establishes a nonlinear relationship between the chemical potential and the nonequilibrium particle density δnm ∝-α1/2 ∝-(-μm)1/2 for magnons under α(＜＜)l.For a large chemical potential,higher-order terms of α must be taken into account.Owing to this nonlinear relationship,the magnon diffusion equation markedly differs from that governing electron spin,which evolves into more complex nonlinear differential equation.We specifically focus on the ferrimagnetic insulator YIG by making a comparison of the spatial distribution of the nonequilibrium magnon density δnm and chemical potential μm between two extreme temperature gradients,namely,▽T～1 K/mm and 104 K/mm,which correspond to μm values on the order of-0.1 μeV and-6.2meV,respectively,while still satisfying the prerequisite α＜1.Given the known temperature gradient distribution,the nonequilibrium magnon density δnm calculated based on our theory is in good agreement with the experimental result.Our theoretical and numerical findings greatly contribute to a profound understanding of the nonequilibrium magnon transport characteristics in magnetic insulators.
关键词
磁振子/非平衡输运/化学势/磁振子扩散方程/玻尔兹曼输运方程Key words
magnon/nonequilibrium transport/chemical potential/magnon diffusion equation/Boltzmann transport equation引用本文复制引用
基金项目
国家自然科学基金(12274258)
美国国家科学基金(DMR1505592)
出版年
2024
国家科技期刊平台
NSTL
万方数据