Two-Dimensional Ferroionics: Conductive Switching Mechanisms And Transition Boundaries in Van Der Waals Layered Material CuInP 2 S 6 .

The recently unfolded ferroionic phenomena in two-dimensional (2D) van der Waals (vdW) copper-indium-thiophosphate (CuInP 2 S 6 or CIPS) have received widespread interest as they allow for dynamic control of conductive switching properties, which are appealing in the paradigm-shift computing. The intricate couplings between ferroelectric polarization and ionic conduction in 2D vdW CIPS facilitate the manipulation and dynamic control of conductive behaviors. However, the complex interplays and underlying mechanisms are not yet fully explored and understood. Here, by investigating polarization switching and ionic conduction in the temperature and applied electric field domains, we discover that the conducting mechanisms of CIPS can be divided into four distinctive states (or modes) with transitional boundaries, depending on the dynamics of Cu ions in the material. Further, we demonstrate that dynamically-tunable synaptic responsive behavior can be well implemented by governing the working-state transition. Our research provides an in-depth, quantitative understanding of the complex phenomena of conductive switching in 2D vdW CIPS with coexisting ferroelectric order and ionic disorder. The developed insights in this work lay the ground for implementing high-performance, function-enriched devices for information processing, data storage, and neuromorphic computing based on the 2D ferroionic material systems. This article is protected by copyright. All rights reserved.