Abstract
Cyclically sheared jammed packings form memories of the shear amplitude at which they were trained by falling into periodic orbits where each particle returns to the identical position in subsequent cycles. While simple models that treat clusters of rearranging particles as isolated two-state systems offer insight into this memory formation, they fail to account for the long training times and multiperiod orbits observed in simulated sheared packings. We show that adding interactions between rearranging clusters overcomes these deficiencies. In addition, interactions allow simultaneous encoding of multiple memories, which would not have been possible otherwise. These memories are different in an essential way from those found in other systems, such as multiple transient memories observed in sheared suspensions, and contain information about the strength of the interactions.
Highlights
Memories in matter can be created in a multitude of ways [1]
Because jammed packings exist in a very rugged, high-dimensional, and complex energy landscape [13], it is astonishing that these systems can find a periodic orbit at all and, that the periodic orbit can be discovered relatively rapidly
The amplitude of the largest previously applied strain can be read out by measuring d, the fraction of hysterons that have changed their state at the end of each readout cycle
Summary
Memories in matter can be created in a multitude of ways [1]. Of interest here is a particular form of memory in which a jammed packing of particles subjected to training by a cyclic quasi-static shear can form a memory of the amplitude at which the shear was applied [2,3,4,5,6,7]. The periodic orbit is disturbed if the shear amplitude is altered so that a memory of the training amplitude can be “read out” by tracking the particle displacements after cycles of increasing strain. This memory formation is reminiscent of the ones found in non-Brownian suspensions [8,9,10,11,12]. For such suspensions, each particle only interacts if it collides with a neighbor; in jammed particle packings, the particles are in enduring contact with their neighbors throughout each cycle. Because jammed packings exist in a very rugged, high-dimensional, and complex energy landscape [13], it is astonishing that these systems can find a periodic orbit at all and, that the periodic orbit can be discovered relatively rapidly
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