Anticorrelation between excitations and locally favored structures in glass-forming systems

Dynamics that are microscopic in space and time, where particles commit to a new position, referred to as excitations, are considered the elementary unit of relaxation in the dynamic facilitation theory of the glass transition. Meanwhile, geometric motifs known as locally favored structures are associated with vitrification in many glassformers. Recent work indicates that the probability of particles being found in both locally favored structures (LFS) and excitations decreases significantly upon supercooling, suggesting an anticorrelation between them [Ortlieb et al., Nat. Commun. 14, 2621 (2023)2041-172310.1038/s41467-023-37793-2]. However, the spatial relationship between excitations and LFS remains unclear. By employing state-of-the-art GPU computer simulations and colloid experiments, we analyze this relationship in model glassformers. We reveal a strong anti-correlation between long-lived LFS and excitations, along with a spatial separation between the two in deeply supercooled liquids. This strong anticorrelation likely arises because well-packed LFS resist local rearrangements, and thus hindering the formation of excitations.