Pareek Puneet, Adhikari Monoj, Dasgupta Chandan, Nandi Saroj Kumar
Tata Institute of Fundamental Research, Hyderabad 500046, India.
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2023 Nov 7;159(17). doi: 10.1063/5.0166404.
Despite the enormous theoretical and application interests, a fundamental understanding of the glassy dynamics remains elusive. The static properties of glassy and ordinary liquids are similar, but their dynamics are dramatically different. What leads to this difference is the central puzzle of the field. Even the primary defining glassy characteristics, their implications, and if they are related to a single mechanism remain unclear. This lack of clarity is a severe hindrance to theoretical progress. Here, we combine analytical arguments and simulations of various systems in different dimensions and address these questions. Our results suggest that the myriad of glassy features are manifestations of two distinct mechanisms. Particle caging controls the mean, and coexisting slow- and fast-moving regions govern the distribution of particle displacements. All the other glassy characteristics are manifestations of these two mechanisms; thus, the Fickian yet non-Gaussian nature of glassy liquids is not surprising. We discover a crossover, from stretched exponential to a power law, in the behavior of the overlap function. This crossover is prominent in simulation data and forms the basis of our analyses. Our results have crucial implications on how the glassy dynamics data are analyzed, challenge some recent suggestions on the mechanisms governing glassy dynamics, and impose strict constraints that a correct theory of glasses must have.
尽管存在巨大的理论和应用兴趣，但对玻璃态动力学的基本理解仍然难以捉摸。玻璃态液体和普通液体的静态性质相似，但其动力学却截然不同。导致这种差异的原因是该领域的核心难题。甚至玻璃态的主要定义特征、它们的含义以及它们是否与单一机制相关都仍不明确。这种不清晰严重阻碍了理论进展。在此，我们结合不同维度各种系统的解析论证和模拟来解决这些问题。我们的结果表明，众多玻璃态特征是两种不同机制的表现。粒子笼效应控制着平均值，共存的慢速和快速移动区域决定了粒子位移的分布。所有其他玻璃态特征都是这两种机制的表现；因此，玻璃态液体的菲克型但非高斯性质并不奇怪。我们发现重叠函数的行为存在从拉伸指数到幂律的转变。这种转变在模拟数据中很突出，并构成了我们分析的基础。我们的结果对如何分析玻璃态动力学数据具有至关重要的意义，对一些近期关于玻璃态动力学控制机制的观点提出了挑战，并对正确的玻璃理论必须具备的条件施加了严格限制。
