Universal Structural Relaxation in Supercooled Liquids

TL;DR

This paper demonstrates that deeply supercooled liquids exhibit a universal spectral shape in their structural relaxation, characterized by a generic high-frequency power law, regardless of molecular structure or interaction type.

Contribution

The study provides a comprehensive comparison of light scattering and dielectric spectra, revealing a universal relaxation lineshape across diverse supercooled liquids.

Findings

Light scattering spectra nearly superimpose across different systems.

Structural relaxation follows an approximate $\omega^{-1/2}$ power law at high frequencies.

Dielectric spectra show more variability, influenced by dipole moments and crosscorrelations.

Abstract

One of the hallmarks of molecular dynamics in deeply supercooled liquids is the non-exponential character of the relaxation functions. It has been a long standing issue if 'universal' features govern the lineshape of glassy dynamics independent of any particular molecular structure or interaction. In the paper, we elucidate this matter by giving a comprehensive comparison of the spectral shape of depolarized light scattering and dielectric data of deeply supercooled liquids. The light scattering spectra of very different systems, e.g. hydrogen bonding and van der Waals liquids but also ionic systems, almost perfectly superimpose and show a generic lineshape of the structural relaxation, approximately following a high frequency power law $\omega^{-1/2}$ . However, the dielectric loss peak shows a more individual shape. In systems with low dipole moment generic behavior is also observed in the dielectric spectra, while in strongly dipolar liquids additional crosscorrelation contributions mask the generic structural relaxation.