低激发极限下的声子瓶颈

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摘要翻译：
在弱激发极限下，对自旋-声子系统的Schroedinger方程进行了简化，数值研究了通过直接声子过程弛豫的二能级系统（自旋）中的声子瓶颈问题。根据精确的多体本征态，得到了弛豫自旋激发p(t)、发射声子n_k(t)等的解。在没有声子阻尼γ{ph}和不均匀展宽的情况下，p(t)接近瓶颈平台P_\infty>0，并出现强阻尼振荡，频率与避免交叉点处的自旋声子分裂δ有关。对于Gamma_{ph}>0的情形，自旋弛豫速率为p(t)->0，但在强瓶颈情况下，自旋弛豫速率比Gamma_{ph}小得多，p(t)是非指数的。超过Delta的非均匀展宽部分缓解了瓶颈，消除了p(t)的振荡。发射声子的线宽和δ随瓶颈的强度即自旋的浓度增加而增加。
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英文标题：
《Phonon bottleneck in the low-excitation limit》
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作者：
D. A. Garanin
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最新提交年份：
2007
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分类信息：

一级分类：Physics        物理学
二级分类：Statistical Mechanics        统计力学
分类描述：Phase transitions, thermodynamics, field theory, non-equilibrium phenomena, renormalization group and scaling, integrable models, turbulence
相变，热力学，场论，非平衡现象，重整化群和标度，可积模型，湍流
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一级分类：Physics        物理学
二级分类：Materials Science        材料科学
分类描述：Techniques, synthesis, characterization, structure.  Structural phase transitions, mechanical properties, phonons. Defects, adsorbates, interfaces
技术，合成，表征，结构。结构相变，力学性质，声子。缺陷，吸附质，界面
--

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英文摘要：
  The phonon-bottleneck problem in the relaxation of two-level systems (spins) via direct phonon processes is considered numerically in the weak-excitation limit where the Schroedinger equation for the spin-phonon system simplifies. The solution for the relaxing spin excitation p(t), emitted phonons n_k(t), etc. is obtained in terms of the exact many-body eigenstates. In the absence of phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the bottleneck plateau p_\infty > 0 with strongly damped oscillations, the frequency being related to the spin-phonon splitting Delta at the avoided crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates the bottleneck and removes oscillations of p(t). The line width of emitted phonons, as well as Delta, increase with the strength of the bottleneck, i.e., with the concentration of spins.
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PDF链接：
https://arxiv.org/pdf/709.0556

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关键词：homogeneous oscillation Transitions Exponential Statistical oscillations Gamma bottleneck Schroedinger 是非