A method for distinguishing between propagons, diffusions, and locons
A method for distinguishing between propagons, diffusions, and locons
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DOI：
10.1063/1.4955420
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发表时间：
2016-07-14
影响因子：
3.2
通讯作者：
Henry, Asegun
中科院分区：
文献类型：
--
作者：
Seyf, Hamid Reza;Henry, Asegun
大多数关于声子输运的直觉来自于对均匀晶体固体的研究，其中原子组成和结构是周期性的。对于这类特定的材料，原子运动方程的解（在谐波极限下）导致了正常振动模式的平面波调制速度场。然而，几十年来，人们已经知道，无论是组成还是结构，只要系统缺乏周期性，振动的正常模式仍然可以确定（在谐波极限），但解决方案采取不同的特性，许多模式可能不是平面波调制。以前的工作已经将振动的类型分为三个主要类别，即传播，扩散和locons。人们可以使用参与率来区分locons，从传播和扩散，这测量了一个模式被本地化的程度。然而，区分传播和扩散仍然是一个挑战，因为两者都是空间离域的。在这里，我们提出了一种新的方法，该方法量化了模式的特征与传播模式相对应的程度，例如，显示平面波调制。这样就可以在传播子和扩散子之间进行清晰和定量的区分。通过定量地解决这个问题，人们现在可以自动化任何任意材料或结构的模式分类，受到原子必须围绕其各自平衡位置稳定振动的单一约束。研究了几个示例测试案例，包括晶体硅和锗，具有不同缺陷浓度的晶体硅，以及非晶硅，锗和二氧化硅。出版社：AIP Publishing
The majority of intuition on phonon transport has been derived from studies of homogenous crystalline solids, where the atomic composition and structure are periodic. For this specific class of materials, the solutions to the equations of motions for the atoms (in the harmonic limit) result in plane wave modulated velocity fields for the normal modes of vibration. However, it has been known for several decades that whenever a system lacks periodicity, either compositional or structural, the normal modes of vibration can still be determined (in the harmonic limit), but the solutions take on different characteristics and many modes may not be plane wave modulated. Previous work has classified the types of vibrations into three primary categories, namely, propagons, diffusions, and locons. One can use the participation ratio to distinguish locons, from propagons and diffusons, which measures the extent to which a mode is localized. However, distinguishing between propagons and diffusons has remained a challenge, since both are spatially delocalized. Here, we present a new method that quantifies the extent to which a mode's character corresponds to a propagating mode, e.g., exhibits plane wave modulation. This then allows for clear and quantitative distinctions between propagons and diffusons. By resolving this issue quantitatively, one can now automate the classification of modes for any arbitrary material or structure, subject to a single constraint that the atoms must vibrate stably around their respective equilibrium sites. Several example test cases are studied including crystalline silicon and germanium, crystalline silicon with different defect concentrations, as well as amorphous silicon, germanium, and silica. Published by AIP Publishing.