Polarization switching in sliding ferroelectrics: the roles of fluctuation and domain wall

Abstract: Sliding ferroelectricity is highly attractive for its low energy barriers and fatigue resistance. As the origin of these exotic properties, its unconventional switching dynamics remains poorly understood: how an electric field drives a perpendicular sliding? Taking $h$-BN bilayer as a model system, its switching dynamics is studied using \textit{ab initio} calculations. The off-diagonal Born effective charge leads to the perpendicular relationship between the electric field and ionic movements. Interestingly, the rules of intrinsic coercive field are distinct between $h$-BN bilayer and conventional ferroelectrics. For $h$-BN bilayer, any perturbation breaking the in-plane symmetry plays a key role to assist the avalanche-like switching dynamics. Moreover, the exotic large off-diagonal Born effective charge near the $P=0$ intermediate state results in a wriggling motion of domain walls in $h$-BN bilayer. Our results reveal the key factors in the ferroelectric switching of sliding ferroelectrics at room temperature.