Edge-Dominated Twist Mechanics at van der Waals Interfaces

Abstract: Despite the pivotal role of twist in modulating physical properties at van der Waals (vdW) interfaces, the mechanics governing torsional response remain poorly understood. Here, we probe twist mechanics at homo- and heterogeneous vdW interfaces, together with their sliding behaviors within a unified experimental framework. For both systems, the peak torque scales nearly linearly with contact area, in contrast to predictions from linear elastic and rigid models. Remarkably, while the sliding friction of the two interfaces diverges by over three orders of magnitude owing to different scaling laws, the corresponding torque follows the same linear scaling and differs by only about twenty-fold. Large-scale atomistic simulations reveal an edge-dominated yielding mechanism for torsional motion, wherein elastic reconstruction shifts the effective load-bearing region toward the edges, eliminating torque from the contact interior. This mechanism contrasts with the bulk-mediated stress transmission governing translational sliding, a distinction rooted in the different loading geometries inherent to the two motion modes, where torsional loading necessitates perimeter actuation, whereas sliding enables center-driven loading. This symmetry-imposed divergence demonstrates that translational and torsional properties cannot be predicted from one another at vdW interfaces, providing critical insights for the design of dynamically reconfigurable micro- and nanoelectromechanical devices.