Strives to understand and control hysteretic response of material systems, wherein applied forces (electric field, stress, optical field) create substantially long-lived metastable states.
Hysteresis is the dependence of the current state of the system on its history. It is a ubiquitous phenomenon in nature, materials, society and economics. Hysteresis enables numerous applications, such as energy storage, information processing, refrigeration, signal processing and control. At the same time, suppressing hysteresis is desired in maximizing coupling of materials to applied fields, optimizing energy efficiency of specific applications, such as solid-state cooling and energy conversion, as well as averting failure of materials subjected to periodic forces.
From a basic scientific perspective, hysteresis is both an old and new topic. It is characteristic of many bulk materials, and its overall behavior can be captured with top-down mathematical models, typically decomposing macroscopic response into collective behavior of individual units. Even in this case, however, the relevant microstructural origins remain actively debated. On the other hand, hysteresis is a vivid example of bottom-up as well as non-equilibrium behavior, emerging in an open system on a length-scale most probably intermediate between atomic- and nano/meso-scales. As such, it is a challenge to both predict and measure hysteretic properties, requiring appropriate multiscale approaches, new experimental methodologies and data analysis, with explicit consideration of non-locality of system response. Moreover, it is almost certain that the hysteresis as an emergent property will be strongly modified with reduction of material dimensions, conceptually similar to quantum size-effects that ignited nanoscience.
The goal of this theme is to reveal, understand and control hysteretic response of nanoscale material systems out of equilibrium. Our particular focus is the emergence of metastable structural, electronic and dipolar states due to applied forces (electric field, stress, optical field), and the concomitant interactions that can stabilize these states on time-scales far exceeding the basic relaxation mechanisms of a material. This a particularly fitting challenge for nanoscience given that the magnitude of the force can vastly exceed its macroscopic counterparts. As such, perhaps any system can be made hysteretic on the nanoscale.
To achieve the theme goals, three specific aims will guide the research:
Aim 1 - Control hysteretic response of layered, soft and liquid polar materials by structural confinement;
Aim 2 - Reveal fundamental mechanisms behind filamentary states and hysteresis in ionic conductors under high electric fields;
Aim 3 - Direct hysteresis in quasiparticle insulators toward “hidden” states unachievable by slow stimulus.
The immediate practical utility of hysteretic response is that the material properties can tuned through appropriate non-thermal stimuli as opposed to changes of the chemical composition. At the same time, hysteretic response itself becomes a probe of “frozen” degrees of freedom and the ensuing non-linear response activated by applied forces. From a fundamental perspective, one of our key aspirations is to develop generalized methodologies to capture, describe, and model hysteretic response at or near the characteristic length-scales of its emergence. Candidate solid-state and soft materials encompass electronic ordering, condensed soft modes, and ions well below the thermal onset of ionic conductivity, are chosen based on their anticipated ability to generate hysteretic response. Successful control over the evolution of the material system in the phase-space defined by these degrees of freedom will enable complex material behavior across a variety of length- and time-scales, will introduce new opportunities to define and redefine nanostructures while conserving atomic structure and will provide unique insight relevant to neuromorphic and energy storage applications. The theme will stimulate further development of experimental and theoretical methods at CNMS, advancing both the core and user programs toward emerging priorities in physics, materials and data analytics, as well as new opportunities relevant to anticipated interest in soft and computational matter initiatives.