Intrinsic\nFerroelectric Switching in Two-Dimensional\nα‑In<sub>2</sub>Se<sub>3</sub>

Two-dimensional\n(2D) ferroelectric semiconductors present opportunities\nfor integrating ferroelectrics into high-density ultrathin nanoelectronics.\nAmong the few synthesized 2D ferroelectrics, α-In<sub>2</sub>Se<sub>3</sub>, known for its electrically addressable vertical polarization,\nhas attracted significant interest. However, the understanding of\nmany fundamental characteristics of this material, such as the existence\nof spontaneous in-plane polarization and switching mechanisms, remains\ncontroversial, marked by conflicting experimental and theoretical\nresults. Here, our combined experimental characterizations with piezoresponse\nforce microscope and symmetry analysis conclusively dismiss previous\nclaims of in-plane ferroelectricity in single-domain α-In<sub>2</sub>Se<sub>3</sub>. The processes of vertical polarization switching\nin monolayer α-In<sub>2</sub>Se<sub>3</sub> are explored with\ndeep-learning-assisted large-scale molecular dynamics simulations,\nrevealing atomistic mechanisms fundamentally different from those\nof bulk ferroelectrics. Despite lacking in-plane effective polarization,\n1D domain walls can be moved by both out-of-plane and in-plane fields,\nexhibiting avalanche dynamics characterized by abrupt, intermittent\nmoving patterns. The propagating velocity at various temperatures,\nfield orientations, and strengths can be statistically described with\na universal creep equation, featuring a dynamical exponent of 2 that\nis distinct from all known values for elastic interfaces moving in\ndisordered media. This work rectifies a long-held misunderstanding\nregarding the in-plane ferroelectricity of α-In<sub>2</sub>Se<sub>3</sub>, and the quantitative characterizations of domain wall velocity\nwill hold broad implications for both the fundamental understanding\nand technological applications of 2D ferroelectrics.