Zaccone Alessio
Department of Physics 'A. Pontremoli', University of Milan, via Celoria 16, 20133 Milano, Italy. Statistical Physics Group, Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, CB3 0AS Cambridge, United Kingdom. Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, CB30HE Cambridge, United Kingdom.
J Phys Condens Matter. 2020 May 13;32(20):203001. doi: 10.1088/1361-648X/ab6e41.
The relaxation dynamics and the vibrational spectra of amorphous solids, such as metal alloys, have been intensely investigated as well separated topics in the past. The aim of this review is to summarize recent results in both these areas in an attempt to establish, or unveil, deeper connections between the two phenomena of relaxation and vibration. Theoretical progress in the area of slow relaxation dynamics of liquid and glassy systems and in the area of vibrational spectra of glasses and liquids is reviewed. After laying down a generic modelling framework to connect vibration and relaxation, the physics of metal alloys is considered where the emergence of power-law exponents has been identified both in the vibrational density of states (VDOS) as well as in density correlations. Also, theoretical frameworks which connect the VDOS to the relaxation behaviour and mechanical viscoelastic response in metallic glasses are reviewed. The same generic interpretative framework is then applied to the case of molecular glass formers where the emergence of stretched-exponential relaxation in dielectric relaxation can be put in quantitative relation with the VDOS by means of memory-function approaches. Further connections between relaxation and vibration are provided by the study of phonon linewidths in liquids and glasses, where a natural starting point is given by hydrodynamic theories. Finally, an agenda of outstanding issues including the appearance of compressed exponential relaxation in the intermediate scattering function of experimental and simulated systems (metal alloys, colloidal gels, jammed packings) is presented in light of available (or yet to be developed) mathematical models, and compared to non-exponential behaviour measured with macroscopic means such as mechanical spectroscopy/rheology.
非晶态固体，如金属合金的弛豫动力学和振动光谱，在过去一直作为两个独立的主题被深入研究。本综述的目的是总结这两个领域的最新成果，试图建立或揭示弛豫和振动这两种现象之间更深层次的联系。综述了液体和玻璃态系统的慢弛豫动力学领域以及玻璃和液体的振动光谱领域的理论进展。在建立了一个连接振动和弛豫的通用建模框架之后，考虑了金属合金的物理性质，其中在振动态密度（VDOS）以及密度相关性中都发现了幂律指数的出现。此外，还综述了将VDOS与金属玻璃中的弛豫行为和机械粘弹性响应联系起来的理论框架。然后，将相同的通用解释框架应用于分子玻璃形成体的情况，其中通过记忆函数方法，介电弛豫中拉伸指数弛豫的出现可以与VDOS建立定量关系。液体和玻璃中声子线宽的研究提供了弛豫和振动之间的进一步联系，其中流体动力学理论给出了一个自然的起点。最后，根据现有的（或有待开发的）数学模型，提出了一系列未解决的问题，包括实验和模拟系统（金属合金、胶体凝胶、堵塞堆积）的中间散射函数中压缩指数弛豫的出现，并与用宏观手段如机械光谱学/流变学测量的非指数行为进行了比较。
