Symmetry and Memory in Driven Disordered Systems

Steadily shearing a non-Brownian suspension forms a memory of direction in its structure, while periodically shearing it forms a memory of amplitude. Our experiments show that these memories coexist and compete within a limited memory capacity. By studying their interplay, we show that these memories can be understood as two facets of the same non-equilibrium physics, arising from the irreversibility of particle interactions. A similar picture is known in amorphous solids. We propose that these competing kinds of memory are a motif for non-equilibrium systems coupled to a scalar drive, and are a basic example of interplay between memories. This connection points to promising questions in other non-equilibrium systems with irreversible dynamics, both non-living and living.