Speaker: Lisa Manning, Faculty Candidate (Princeton University)
Both solids and fluids can flow under applied stress. In crystalline solids, flow occurs via particle rearrangements controlled by a population of dislocations, while in fluids, particle rearrangements occur everywhere throughout the material. In disordered solids, flow generally occurs via localized rearrangements, but no one has been able to identify a population of flow defects, analogous to dislocations, that are structurally different from the rest of the system and more susceptible to flow. It has therefore remained unclear whether a solid-like or fluid-like description is more appropriate for describing flow in such systems. By analyzing the low-energy vibrational modes in a model glass, we have identified a population of structurally distinct, long-lived ``soft spots'', and we show that particle rearrangements are initiated at these spots.
These results support a solid-like description of flow controlled by a population of localized flow defects in glassy materials, and provide new insight into related problems, such as the origin of localization at low frequencies and the development of predictive continuum models for solids.