The Interplay between Memory Training and Stability in Jammed Solids*

Memory formation by cyclic shear is one of the most fascinating yet unclear mechanical properties of jammed solids. When repeatedly sheared with cycles of a certain strain amplitude, the system reaches a limit cycle after which no further changes occur under the same cyclic shear transformation. Although memory encoding has been observed both in simulations and experiments of amorphous solids, it is still unclear what triggers memory formation in real space and how this phenomenon relates to the stability of the system. We perform cyclic shear training on marginally stable and highly stable packings, the latter being produced via a constrained minimization of both positional and radial degrees of freedom. We further characterize memory encoding in both systems and find that while marginally stable packings easily encode memories for a wide range of strain amplitudes, highly stable packings need to lose their stability and become marginally stable to be able to encode a memory.