First-Principles Insights into Layer-by-Layer Polarization Reversal in van der Waals Ferroelectric CuInP₂S₆

Two-dimensional (2D) van der Waals (vdW) ferroelectric materials, such as CuInP₂S₆ have attracted significant interest due to the unique displacements of Cu⁺ ions both within the layers and across the vdW gap, which enable robust ferroelectricity even in the monolayer limit. In this work, we employ first-principles calculations to investigate various structural candidates of CuInP₂S₆, including the paraelectric centrosymmetric P-31c and C2/c phases. Phonon-instability analysis of these paraelectric structures reveals the polarization-switching pathways and their relationship to the respective ferroelectric ground states, suggesting that ferroelectric polarization in CuInP₂S₆ can be switched in a layer-by-layer manner. Furthermore, by analyzing Cu-ion displacements and layer-resolved polarization, we uncover an asynchronous switching mechanism that can be tuned through stacking engineering.^[1] These findings provide new microscopic insights into controllable ferroelectric switching and polarization dynamics in layered vdW ferroelectrics.

^[1] Pegah Mohammadi, and Sobhit Singh, Physical Review B 112, 125205 (2025).