Structural signatures evidenced in dynamic crossover phenomena in metallic glass-forming liquids

Abstract

Molecular dynamics simulations were performed to investigate dynamic evolution in metallic glass-forming liquids during quenching from high temperature above melting point down to supercooled region. Two crossover temperatures TA and TS (TA > TS) are identified, and their physical meanings are clarified. TA and TS are found to be not only the sign of dynamic crossover phenomena but also the manifestation of two key structure correlation lengths ξs. As temperature decreases below TA, ξs goes beyond the nearest-neighbor distance, resulting in the Arrhenius-to-non-Arrhenius transition of structural relaxation time and the failure of Stokes-Einstein (SE) relation. As TS is traversed, the increase rate of ξs reaches the maximum, leading to the simultaneous appearance of dynamical heterogeneity and fractional SE relation. It is further found that structure correlation increases much faster than dynamic correlation, playing a role of structural precursor for dynamic evolution in liquids. Thus, a structural link is established for deeper understanding dynamic crossover phenomena.