Lifetime of dynamical heterogeneity in a highly supercooled liquid

We numerically examine dynamical heterogeneity in a highly supercooled three-dimensional liquid via molecular-dynamics simulations. To define the local dynamics, we consider two time intervals, $\tau_\alpha$ and $\tau_{\text{ngp}}$. $\tau_\alpha$ is the $\alpha$ relaxation time, and $\tau_{\text{ngp}}$ is the time at which non-Gaussian parameter of the van Hove self-correlation function is maximized. We determine the lifetimes of the heterogeneous dynamics in these two different time intervals, $\tau_{\text{hetero}}(\tau_\alpha)$ and $\tau_{\text{hetero}}(\tau_{\text{ngp}})$, by calculating the time correlation function of the particle dynamics, i.e., the four-point correlation function. We find that the difference between $\tau_{\text{hetero}}(\tau_\alpha)$ and $\tau_{\text{hetero}}(\tau_{\text{ngp}})$ increases with decreasing temperature. At low temperatures, $\tau_{\text{hetero}}(\tau_\alpha)$ is considerably larger than $\tau_{\alpha}$, while $\tau_{\text{hetero}}(\tau_{\text{ngp}})$ remains comparable to $\tau_{\alpha}$. Thus, the lifetime of the heterogeneous dynamics depends strongly on the time interval.