Multi-time correlation analysis for heterogeneous dynamics in glass-forming liquids

引入密度相关函数的多时间扩展来揭示玻璃形成液体的动力学非均质性的时间信息。本研究中使用的多时间相关函数类似于多维非线性光谱学中分析的高阶响应函数。我们证实，二维表征对动力学异质性很敏感，并且这些表征揭示了在广泛的时间尺度上存在的相关运动的耦合。从这一分析出发，我们系统地评估了动力非均质性的寿命及其温度依赖性。此外，我们还研究了动力学非均质寿命在粘度和自扩散常数之间的Stokes-Einstein （SE）关系的破坏中的物理作用。在高度过冷液体中，SE关系的大违逆以比动力学非均质寿命更长的时间尺度为特征。

A multi-time extension of a density correlation function is introduced to reveal temporal information about dynamical heterogeneity in glass-forming liquids. A multi-time correlation function utilized in this study is analogous to the higher-order response function analyzed in multidimensional nonlinear spectroscopy. We confirm that the two-dimensional representations are sensitive to the dynamical heterogeneity and that these reveal the couplings of correlated motions, which exist over a wide range of time scales. From this analysis, we evaluated the lifetime of the dynamical heterogeneity and its temperature dependence systematically. Furthermore, we examine the physical role of the lifetime of dynamical heterogeneity in the violation of the Stokes-Einstein (SE) relation between viscosity and self-diffusion constant. Large violations of the SE relation are characterized by time scales longer than the lifetime of the dynamical heterogeneity in highly supercooled liquids.