A dynamic crossover with possibly universal dynamic signatures in simple glass-forming liquids

On approaching the glass transition, the structural relaxation of glass-forming liquids slows down drastically, along with a significant growth of dynamic heterogeneity. Recent studies have achieved substantial advancements in elucidating the quantitative correlations between structural relaxation and dynamic heterogeneity. Here, we present the discovery of a novel dynamic crossover with possibly universal dynamic signatures by investigating the relationship between structural relaxation and dynamic heterogeneity. Specifically, the structural relaxation time at the dynamic crossover τ_c is equal to the time scale for the maximum non-Gaussian parameter, which could serve as a quantitative characterization of dynamic heterogeneity. The degree of dynamic heterogeneity at the crossover is approximately equivalent across all investigated glass-forming liquids, leading to a scaling collapse between structural relaxation and dynamic heterogeneity. Moreover, the mean squared displacement at the structural relaxation time is nearly constant across different temperatures as long as the structural relaxation time does not exceed τ_c. We further observe that the temperature at the dynamic crossover is lower than the onset temperature of slow dynamics. Our findings thus suggest the existence of a novel dynamic crossover with possibly universal dynamic signatures in glass-forming liquids, which merits in-depth investigations.