Chemical Physics Department, Weizmann Institute of Science, Rehovot 7610001, Israel.
Institute for Theoretical Physics, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
Proc Natl Acad Sci U S A. 2017 Jul 11;114(28):7289-7294. doi: 10.1073/pnas.1704403114. Epub 2017 Jun 27.
Identifying heterogeneous structures in glasses-such as localized soft spots-and understanding structure-dynamics relations in these systems remain major scientific challenges. Here, we derive an exact expression for the local thermal energy of interacting particles (the mean local potential energy change caused by thermal fluctuations) in glassy systems by a systematic low-temperature expansion. We show that the local thermal energy can attain anomalously large values, inversely related to the degree of softness of localized structures in a glass, determined by a coupling between internal stresses-an intrinsic signature of glassy frustration-anharmonicity and low-frequency vibrational modes. These anomalously large values follow a fat-tailed distribution, with a universal exponent related to the recently observed universal [Formula: see text] density of states of quasilocalized low-frequency vibrational modes. When the spatial thermal energy field-a "softness field"-is considered, this power law tail manifests itself by highly localized spots, which are significantly softer than their surroundings. These soft spots are shown to be susceptible to plastic rearrangements under external driving forces, having predictive powers that surpass those of the normal modes-based approach. These results offer a general, system/model-independent, physical/observable-based approach to identify structural properties of quiescent glasses and relate them to glassy dynamics.
识别玻璃中的不均匀结构（如局部软点）并理解这些系统中的结构-动力学关系仍然是重大的科学挑战。在这里，我们通过系统的低温展开，推导出玻璃态系统中相互作用粒子的局部热能（由热涨落引起的平均局部势能变化）的精确表达式。我们表明，局部热能可以达到异常大的值，与玻璃中局部结构的柔软度成反比，这由内部应力之间的耦合决定——玻璃受挫的内在特征——非谐性和低频振动模式。这些异常大的值遵循胖尾分布，具有与最近观察到的准局部低频振动模式的通用[公式：见文本]态密度相关的通用指数。当考虑空间热能场（“柔软度场”）时，这种幂律尾部表现为高度局部化的斑点，其柔软度明显高于周围环境。这些软点在外部驱动力作用下容易发生塑性重排，其预测能力超过基于正常模式的方法。这些结果提供了一种通用的、与系统/模型无关的、基于物理/可观测的方法来识别静止玻璃的结构特性，并将其与玻璃动力学联系起来。
