Isolating the Enhanced Memory Capacity of a Glassy System

Recent studies of glassy materials have shown how cyclic deformations can form memories of strain. We explore how choices of preparation and driving protocol can reveal dramatically different aspects of a system's memory capacity. We simulate a system of multiple rearranging soft spots subject to cyclic shear, modeled as hysterons. For hysterons with cooperative (ferromagnetic) interactions, symmetric driving (e.g. both positive and negative shear strain) reveals a return-point memory of multiple strains observed previously in experiments and molecular dynamics simulations. By contrast, asymmetric driving (e.g. only positive shear strains, or only compressive loading) prevents these memories. However, when frustrated interactions are introduced, a different mechanism takes the place of return-point memory and restores the capacity for multiple values. Our work suggests that this more robust form of memory can be a leading-order signature of frustration.