  The deformation mechanism in amorphous solids subjected to external shear
remains poorly understood because of the absence of well-defined topological
defects mediating the plastic deformation. The notion of soft spots has emerged
as a useful tool to characterize the onset of irreversible rearrangements and
plastic flow, but these entities are not clearly defined in terms of geometry
and topology. In this study, we unveil the phenomenology of recently
discovered, precisely defined topological defects governing the microscopic
mechanical and yielding behavior of a model 3D glass under shear deformation.
We identify the existence of vortex-like and anti-vortex-like topological
defects within the 3D non-affine displacement field. The number density of
these defects exhibits a significant anti-correlation with the plastic events,
with defect proliferation-annihilation cycles matching the alternation of
elastic-like segments and catastrophic plastic drops, respectively.
Furthermore, we observe collective annihilation of these point-like defects via
plastic events, with large local topological charge fluctuations in the
vicinity of regions that feature strong non-affine displacements. We reveal
that plastic yielding is driven by several large sized clusters of net negative
topological charge, the massive annihilation of which triggers the onset of
plastic flow. These findings suggest a geometric and topological
characterization of soft spots and pave the way for the mechanistic
understanding of topological defects as mediators of plastic deformation in
glassy materials.
