From sub-aging to hyper-aging in structural glasses

TL;DR

This paper develops non-equilibrium scaling laws for aging in glass formers, revealing different regimes such as simple aging, sub-aging, and hyper-aging depending on quench depth, and supports these with a schematic model fitting simulation data.

Contribution

It introduces a unified framework combining Onsager's theory with glassy scaling laws to describe aging regimes in glasses, including hyper-aging phenomena.

Findings

Different aging regimes are predicted based on quench depth.

Hyper-aging is characterized by super-linear growth of relaxation time.

The model fits simulation data for density-quenched particles.

Abstract

We demonstrate non-equilibrium scaling laws for the aging dynamics in glass formers that emerge from combining a recent application of Onsager's theory of irreversible processes with the equilibrium scaling laws of glassy dynamics. Different scaling regimes are predicted for the evolution of the system's structural relaxation time $\tau$ with age (waiting time $t_w$), depending on the depth of the quench from the liquid into the glass: \emph{simple aging} ($\tau\sim t_w$) applies for quenches close to the critical point of mode-coupling theory (MCT) and implies \emph{sub-aging} ($\tau\approx\ t_w^\delta$ with $\delta<1$) as a broad cross-over for quenches to nearly-arrested equilibrium states; \emph{hyper-aging} (or \emph{super-aging}, $\tau\sim t_w^{\delta'}$ with $\delta'>1$) emerges for quenches deep into the glass. The latter is cut off by non-mean-field fluctuations that we account for within a recent extension of MCT, the stochastic $\beta$-relaxation theory (SBR). We exemplify the scaling laws by a schematic model that allows to quantitatively fit recent simulation results for density-quenched hard-sphere-like particles.