Van der Waals ferroelectricity
Layered ferroelectric polytypes
Van der Waals ferroelectrics emerge from the interlayer symmetry in specific layered polypes, like the rhombohedral 3R phases of hBN or transition metal dichalcogenides (TMDCs) like WS2.
These layered polytypes exhibit fast, high-endurance switching based on interfacial dislocation motion, resulting in less defect-mediated degradation compared with traditional ferroelectrics (Link1 , Link2). For TMDCs, the 3R phase appears to exhibit increased charge carrier mobility compared to the common 2H phase (Link3), bulk photovolatic effect (Link4), with additive interface-by-interface polarization for programmable multi-state retention (link5).
We are developing large-area synthesis of 3R-phase 2D materials, studying their domain-wall dynamics, and exploring their potential applications in optoelectronic devices.
Anti-ferroelectric moiré
Creating a twisted moiré heterostructure near the 3R alignment results in a ferroelectric moiré pattern, characterized by two opposing out-of-plane polarizations per unit cell. This structure enables the development of a tunable electrostatic proximity moiré or an adjustable array of quantum dots, offering potential for nanoscale device applications.
Our research focuses on understanding the properties of the ferroelectric moiré, investigating its thermal stability, and applying it within van der Waals heterostructures to explore new optoelectronic and quantum functionalities.
For a study of thermal stability, check out M. Hocking et al., Journal of Applied Physics (2024).