Memory formation in cyclically deformed amorphous solids and sphere assemblies

TL;DR

This paper investigates how amorphous solids and sphere assemblies encode and retrieve multiple memories through cyclic shear deformation, revealing conditions for non-transient memory storage linked to loop reversibility.

Contribution

It demonstrates that multiple memories can be stored non-transiently in sphere assemblies and links this to loop reversibility, expanding understanding of memory effects in amorphous materials.

Findings

Multiple memories can be robustly retrieved using various read protocols.

Large amplitude shear erases stored memories.

Non-transient multiple memory storage is associated with loop reversibility.

Abstract

We study a model amorphous solid that is subjected to repeated athermal cyclic shear deformation. It has previously been demonstrated that the memory of the amplitudes of shear deformation the system is subjected to (or trained at) is encoded, and can be retrieved by subsequent deformation cycles that serve as read operations. Here we consider different read protocols and measurements and show that single and multiple memories can be robustly retrieved through these different protocols. We also show that shear deformation by a larger amplitude always erases the stored memories. These observations are similar to those in experiments with non-Brownian colloidal suspensions and corresponding models, but differ in the possibility of storing multiple memories non-transiently. Such a possibility has been associated with the presence of cycles of transitions that take place in the model amorphous solids, between local energy minima. Here, we study low density sphere assemblies which serve as models for non-Brownian colloidal suspensions, under athermal deformation, and identify a regime where multiple memories are stored in these systems as well non-transiently. We show that the regime where storing multiple memories non-transiently corresponds to the presence of loop reversibility, rather than point reversibility of configurations under cyclic deformation.