Universal Scaling in the Aging of the Strong Glass Former SiO${}_2$

Abstract

We show that the aging dynamics of a strong glass former displays a strikingly simple scaling behavior, connecting the average dynamics with its fluctuations, namely the dynamical heterogeneities. We perform molecular dynamics simulations of SiO${}_2$ with BKS interactions, quenching the system from high to low temperature, and study the evolution of the system as a function of the waiting time $t_{\mathrm{w}}$ measured from the instant of the quench. We find that both the aging behavior of the dynamic susceptibility ${\chi }_4$ and the aging behavior of the probability distribution $P(f_{\mathrm{s},\mathbf{r}})$ of the local incoherent intermediate scattering function $f_{\mathrm{s},\mathbf{r}}$ can be described by simple scaling forms in terms of the global incoherent intermediate scattering function $C$. The scaling forms are the same that have been found to describe the aging of several fragile glass formers and that, in the case of $P(f_{\mathrm{s},\mathbf{r}})$, have been also predicted theoretically. A thorough study of the length scales involved highlights the importance of intermediate length scales. We also analyze directly the scaling dependence on particle type and on wavevector $q$, and find that both the average and the fluctuations of the slow aging dynamics are controlled by a unique aging clock, which is not only independent of the wavevector $q$, but is the same for O and Si atoms.

13 pages, 21 figures (postscript)

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