Topological phase transition in metallic glass formers

Metallic glass-forming systems exhibit complex dynamic behaviors during the glass transition. Understanding the dynamic nature of metallic glasses and supercooled liquids is a crucial issue in the study of glassy physics. Topological order provides a novel perspective for re-examining the dynamics of glassy systems and elucidating the physical essence of the glassy state and glass transition. In this study, the microscopic dynamics of CuZr melts in the glass transition are investigated using molecular dynamics simulations. The single-particle dynamic characteristics in the supercooled CuZr melt are the random jump motions of atoms after a long-term caging period. To capture these dynamics, the displacement vector field is constructed based on the spatiotemporal distribution of these jump events. The simulation results reveal that there exist the numerous vortex structures in the displacement vector field. Notably, the vortex formation rate, which is defined as the number of vortices generated per unit time, exhibits a sharp drop near the glass transition temperature. The probability distribution of vortex formation rate displays a bimodal pattern on the drops, indicating the coexistence of two different dynamical states related to vortex formation. Multiple high-strain events are observed surrounding these vortices. It is found that the two vortex states during the transition exhibit markedly different characteristic ratios of vortices to high-strain events (1∶4 <i>vs</i> 1∶8), indicating a change in the coupling strength between vortex formation and high-strain activity. The high-strain events predominantly form in the regions between positive and negative vortices, and the specific quantitative relationship between vortices and high-strain events indirectly reflects the presence of strongly interacting vortex-antivortex pairs in the melt. During the vortex state transition, the vortex-to-high-strain-event ratio suddenly doubles, which means that this transition is not only a sudden change in the rate of vortex formation, but also an enhancement of the interactions between vortex-antivortex pairs, representing a change in global topological properties. These findings demonstrate that the vortex transition exhibits the characteristics of a topological phase transition, thereby predicting the existence of a topological phase transition in the displacement vector field of metallic glass-forming systems. Further speculation suggests that vortices and high-strain events are related to multiple secondary relaxation processes. This study provides a new perspective for understanding the dynamics of glass-forming systems and the glass transition.