Layers Slide on Their Own: Warm Motion in Two-Dimensional Crystals express
Two sheets of paper stacked together start to creep ever so slightly over each other when heated. That's roughly how layers of molybdenum disulfide, a material one atom thick, behave. At room temperature, they spontaneously slide at a speed of about one meter per second.
Previously, it was thought that shifting layers required overcoming a barrier, like dragging a heavy box over a threshold. But atomic-level calculations show there's almost no barrier. The motion doesn't happen as a shift of the whole sheet but as a wave of rearrangement at the boundaries between regions with different orientations. It's like a wrinkle moving across a carpet without the carpet itself shifting.
This behavior opens the way to memory devices where information is written by shifting layers with almost no energy cost.
Original abstract
as written by the authors arXiv:2604.20277
Sliding ferroelectrics built from stacked nonpolar monolayers enable out-of-plane polarization and unconventional switching via interlayer sliding, yet the microscopic sliding dynamics remain unclear. Using machine-learning molecular dynamics, we reveal spontaneous thermally driven interlayer sliding in ferroelectric MoS2 moir\'e superlattices, with relative velocities on the order of 1 m/s at 300 K. Instead of rigid translation of the entire bilayer, the motion appears as a global drift of the moir\'e pattern. Such thermally driven sliding is inconsistent with the meV/atom-scale rigid-sliding barrier. In contrast, when constrained relaxation is allowed, the sliding proceeds along an almost barrierless pathway that directly reproduces the global drift of the moir\'e pattern. Furthermore, sulfur vacancies trigger a sliding-to-pinning transition, with about 0.1% S vacancies already sufficient to convert the long-range sliding into localized oscillations. Notably, these phenomena are not restricted to small twist angles, but arise generically in twisting-induced multidomain structures. These results reveal that the sliding process is governed by a domain-wall-mediated collective reconstruction pathway with an ultralow barrier, rather than rigid layer translation, deepening the understanding of microscopic dynamics in moir\'e superlattices and sliding ferroelectrics.
The speed of spontaneous layer sliding at room temperature is about 1 m/s, similar to a leisurely walking person.