Rethinking phonons: The issue of disorder
Rethinking phonons: The issue of disorder
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DOI：
10.1038/s41524-017-0052-9
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发表时间：
2017-11
影响因子：
9.7
通讯作者：
H. Seyf;Luke Yates;Thomas L. Bougher;S. Graham;B. Cola;T. Detchprohm;M. Ji;Jeomoh Kim;R. Dupuis;Wei-Ling Lv;A. Henry
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文献类型：
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作者：
H. Seyf;Luke Yates;Thomas L. Bougher;S. Graham;B. Cola;T. Detchprohm;M. Ji;Jeomoh Kim;R. Dupuis;Wei-Ling Lv;A. Henry
目前对声子的理解将它们视为传播和散射的平面波/原子振动的准粒子。问题是，从概念上讲，当引入任何水平的无序时，无论是成分还是结构，固体中振动模式的特征都会发生变化，但几乎所有的理论处理都继续假设声子仍然是波。例如，声子对合金热导率（TC）的贡献依赖于这一假设，并且最常从虚晶近似（VCA）计算。在某些情况下，可以获得很好的一致性，但在许多情况下，无论是定量还是定性，它都失败了。在这里，我们表明，传统的理论和理解的声子需要修改，因为关键的假设，所有的声子/正常模式类似于平面波与明确定义的速度是不再有效时，引入无序。令人惊讶的是，在杂质浓度的前几个百分比内，声子的性质发生了显着变化，超过这个百分比，声子更接近于非晶材料中发现的模式。然后，我们利用一个不同的理论，可以处理模式与任何字符和实验证实其新的见解。
Current understanding of phonons treats them as plane waves/quasi-particles of atomic vibration that propagate and scatter. The problem is that conceptually, when any level of disorder is introduced, whether compositional or structural, the character of vibrational modes in solids changes, yet nearly all theoretical treatments continue to assume phonons are still waves. For example, the phonon contributions to alloy thermal conductivity (TC) rely on this assumption and are most often computed from the virtual crystal approximation (VCA). Good agreement is obtained in some cases, but there are many instances where it fails—both quantitatively and qualitatively. Here, we show that the conventional theory and understanding of phonons requires revision, because the critical assumption that all phonons/normal modes resemble plane waves with well-defined velocities is no longer valid when disorder is introduced. Here we show, surprisingly, that the character of phonons changes dramatically within the first few percent of impurity concentration, beyond which phonons more closely resemble the modes found in amorphous materials. We then utilize a different theory that can treat modes with any character and experimentally confirm its new insights.