Strives to understand and control hysteretic response of material systems, wherein applied forces (electric field, stress, optical field) create substantially long-lived metastable states.
Tailoring materials responses in time-dependent fields to take advantage of hysteretic properties (dependence of the current state of the system on its history) has been paramount for modern technology. In particular, we have utilized fields to control energy flow in hysteretic materials to enable advances ranging from energy storage to information processing. For example, applying electrical stress to a conventional binary oxide has been shown to create a material equipped with intrinsic memory and capable of computation. Also, recent studies have observed ultra-fast time-varying perturbation of material structure may dramatically enhance the superconducting properties, possibly to as high as room temperature. It is clear that such a progressive departure from an equilibrium state under an applied field can fundamentally transform a material and its response. The structure and dynamics in materials away from equilibrium is, in general, path-dependent on the specific history of applied stimulus, while specific structures (such as interface) on molecular and atomic scale can define macroscopically observed response. Therefore, it is clear that at the nanoscale, we need to understand non-equilibrium response of material systems.
The overarching goal of the hysteretic nanomaterials theme is to understand the response of nanostructured materials to applied forces, so as to control energy transport on the nanoscale and create long-lived metastable states with improved or unique functionalities. To achieve this goal, the theme is organized into three specific aims, emphasizing, correspondingly, the force, the response, and the relaxation dynamics of driven nanostructured materials – all integral parts of their hysteretic response. In Aim 1, we focus on revealing interfacial dynamics in polar materials under an electric field. Here, the stability, structure, electric fields and electrochemical effects are at the heart of the control of interfaces over proximate materials. Thus, by fine control of the electric field and structure near an active, dynamic interface, we can begin to understand the effects of interfaces on dynamics in polar materials. In Aim 2, we seek to understand the fundamentals of ion transport leading to metastable states and hysteresis. Here we will achieve control over metastable ionic states by decoupling energy flows used to activate ionic motion, through the use of specific excitation as well as by the judicious choice of material mechanisms, where the characteristic energy scales of the responsive degrees of freedom can be substantially separated. In Aim 3, the goal is to control metal-insulator transitions in quasiparticle insulators via non-equilibrium response. Here the focus is on non-linear response of electronic degrees of freedom, emerging in quasiparticle insulators subjected to strong fields and currents.
Hysteresis is a vivid example of non-equilibrium behavior emerging in length-scales often intermediate between atomic- and nano/meso-scales. As such, it is a challenge to both predict and measure hysteretic properties. In pursuit of our overarching goal, this theme will develop new multiscale theoretical approaches to capture the ionic, dipolar and electronic materials in applied fields, 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 the size-effects that ignited nanoscience. Beyond envisioned fundamental impact, the theme will stimulate further development of microscopy and theoretical capabilities at CNMS, as well as deeper understanding of non-equilibrium response, thereby advancing new capabilities toward development of future user programs. Additionally, insight into hysteretic response, electronic ordering in materials, dipolar interactions, and non-equilibrium ionic currents can translate into emerging paradigms for energy storage, computing and control.