Memory formation in matter

Abstract

Memory formation in matter is a theme of broad intellectual relevance; it sits at the interdisciplinary crossroads of physics, biology, chemistry, and computer science. Memory connotes the ability to encode, access, and erase signatures of past history in the state of a system. Once the system has completely relaxed to thermal equilibrium, it is no longer able to recall aspects of its evolution. Memory of initial conditions or previous training protocols will be lost. Thus many forms of memory are intrinsically tied to far-from-equilibrium behavior and to transient response to a perturbation. This general behavior arises in diverse contexts in condensed matter physics and materials: phase change memory, shape memory, echoes, memory effects in glasses, return-point memory in disordered magnets, as well as related contexts in computer science. Yet, as opposed to the situation in biology, there is currently no common categorization and description of the memory behavior that appears to be prevalent throughout condensed-matter systems. Here we focus on material memories. We will describe the basic phenomenology of a few of the known behaviors that can be understood as constituting a memory. We hope that this will be a guide towards developing the unifying conceptual underpinnings for a broad understanding of memory effects that appear in materials.

Embedding orthogonal memories in a colloidal gel through oscillatory shear

“…Indeed, similar memory effects have been found in experiments and simulations of model amorphous systems [2,9,10], granular systems [11], and glasses [12][13][14][15]. The interactions between particles can vary and even the nature of the reversibility can vary for different systems [9,[16][17][18][19][20]. The core idea of particles rearranging and exploring possible states to find a reversible one still applies, regardless of the specifics of the system.…”

Chiral domain walls of Mn3Sn and their memory

“…We will show that this is caused by residual minority domains promoting a specific chirality. This last observation constitutes a new case of memory formation in condensed matter recording a direction [27]. Fig.…”

“…In the first case the PHE signals are positive, in the second are negative. We note that this is a phenomenon belonging to the category dubbed memory of direction [27]. By subtracting the two sets of data or adding them, one can extract the symmetric ( fig.…”

Potential energy states and mechanical properties of thermally cycled binary glasses

“…One of the findings of the present study is the appearance of well-defined steady states with particular energy levels and nearly reversible dynamics. This, in turn, opens the question of memory formation in such systems similar to memory effects reported in periodically driven glasses [39]. For example, thermally cycled glasses with a particular thermal amplitude might continue to expand and contract reversibly if the thermal amplitude is reduced or instead undergo structural relaxation if the thermal amplitude is increased.…”