Sliding and superlubric twisting ferroelectric transition in bilayer HfO2

Despite progress in HfO ₂ thin-film ferroelectrics, issues such as fatigue and high coercive fields persist, and the dynamics of emerging twisted ferroelectricity remain largely unexplored. Here, we explore how interlayer sliding and twisting in bilayer HfO ₂ enables low barrier switching pathways. Among 144 sliding configurations, two exhibit strong in-plane polarization (2360 pC/m) with a low switching barrier of 3.19 meV/atom. Twisting generates polar textures associated with moiré patterns and quasi-flat bands, which drive ferroelectricity via a soft zone-center optical mode, as revealed by machine-learning-assisted first-principles calculations. At twist angles of 21.79° and 27.80°, switching barriers drop to 0.58 and 0.06 meV/atom, indicating superlubric-like ferroelectric transitions. Notably, the 46.83° twisted bilayer shows an almost barrier-free polar evolution (0.009 meV/atom), attributed to sharply enhanced zone-center phonon linewidths. Our findings establish a moiré-engineered, ultra-low-energy switching route for 2D ferroelectric applications.