Multiple and transforming vibrational identities of atoms in amorphous solids.

This article focuses on classifying atoms in an amorphous Cu₅₀Zr₅₀ metallic glass based on their full-frequency vibrational modes to better understand their roles in plastic deformation. Atoms are categorized into low-frequency (LAs), subhigh-frequency (SHAs), and high-frequency atoms (HAs), each exhibiting distinct structural, mechanical, and spatial characteristics: LAs are structurally unstable and tend to cluster, SHAs form stable, dense backbones, and HAs originate from compressed atomic pairs and are mechanically unstable. During mechanical loading, plastic rearrangements initially occur at LAs and progressively shift to HAs, with atoms dynamically transforming between these vibrational identities, often overlapping spatially without clear boundaries. This vibrational-mode-based classification reveals a complex, spatiotemporally evolving atomic landscape in amorphous solids that extends beyond the traditional soft-spot versus hard-matrix paradigm, offering deeper insight into the atomic origins of amorphous plasticity.