Robust local dipole and weak inter-dipole coupling in two-dimensional ferroelectric CuInP2S6 monolayers

In this work, we uncover the physical origin of room-temperature stable and small-sized ferroelectric domains in monolayer CuInP2S6. Our phenomenological model, accurately fitted by first-principles datasets, elucidates the physical origins of previously reported order–disorder transitions and scale-free behavior in the studied system. Unlike conventional perovskite ferroelectrics, the ferroelectricity in monolayer CuInP2S6 stems from spontaneous intra-cell polar distortions with negligible inter-dipole coupling. While antiferroelectric ordering emerges as the ground state, its thermal stability competes with scale-free and distorted ferroelectric configurations. We quantitatively clarify this mechanism through our modeling, demonstrating how the degeneracy of metastable states enables coexisting order parameters across multiple length scales. This work fundamentally distinguishes weak-correlation ferroelectricity from conventional cooperative mechanisms, offering promising design principles for nanoscale ferroelectric devices, with particular promise for high-density memory applications.