The Return-Point Memory of a Soft Jammed Solid

A soft 2D jammed material can form memories of past deformations. Our experiments cyclically shear a material made of repulsive particles at an oil-water interface, observing the motion of many particles. After many cycles, the system reaches an approximately steady state in which few new rearrangements are created. We show that in this state the system has a memory of past strain amplitudes that is similar to return-point memory in ferromagnets and many other condensed-matter systems. While the system may appear to be changed upon decreasing the strain amplitude, returning to the previous value restores the system's state, allowing readout of multiple encoded memories. We discuss similarities and differences with memory behaviors in non-jammed suspensions.