Crystalline Shielding Localizes Memory in Jammed Systems Under Oscillatory Shear

Amorphous, jammed systems are abundant in nature and used often to process and produce materials. However, the way in which these systems' disordered and multi-scale structure evolves under the application of stress, eventually resulting in catastrophic failure, has yet to be fully elucidated. In particular, understanding how microscopic rearrangement gives rise to macroscopic structural and rheological signatures in disordered systems is vital for the prediction and characterization of yield and for the study of how memory is stored in disordered materials. Here, we investigate the evolution of local structural homogeneity on an individual particle level in amorphous, jammed two-dimensional colloidal systems under oscillatory shear, and relate this evolution to rearrangement, memory, and macroscale rheological measurements. We identify a new structural metric, crystalline shielding, that is predictive of rearrangement propensity of individual particles under shear. We use this metric to identify localized regions of the system in which the material's memory of its preparation is preserved. Our results contribute to a growing understanding of how local structure relates to dynamic response and memory in disordered and jammed systems.