Superlubric Motion of Wavelike Domain Walls in Sliding Ferroelectrics

Sliding ferroelectrics constructed from stacked nonpolar monolayers enable out-of-plane polarization in two dimensions with exceptional properties. However, the widely accepted switching mechanism, involving synchronized long-distance in-plane translation of entire atomic layers, contradicts experimental findings. We demonstrate that this spinodal decompositionlike homogeneous switching process violates Neumann's principle and is therefore highly improbable. Instead, polarization reversal relies on symmetry-breaking domain walls (DWs) and the tensorial nature of Born effective charges, highlighting the quantum nature of sliding ferroelectrics. We reveal that wide, wavelike DWs coherently propagate, a stark departure from the narrow DW mechanism recognized for decades. These wavelike DWs exhibit superlubric dynamics, achieving ultrahigh velocities of approximately 4000  m/s at room temperature and displaying an anomalous cooling-promoted switching speed. The unexpected emergence of DW superlubricity presents new avenues for enhancing key performance metrics and offers exciting opportunities for applications in cryogenic environments.