Negative differential friction coefficients of two-dimensional commensurate contacts dominated by electronic phase transition

Friction force (f) usually increases with the normal load (N) macroscopically, according to the classic law of Da Vinci–Amontons (f = µN), with a positive and finite friction coefficient (µ). Herein near-zero and negative differential friction (ZNDF) coefficients are discovered in two-dimensional (2D) van der Waals (vdW) magnetic CrI₃ commensurate contacts. It is identified that the ferromagnetic–antiferromagnetic phase transition of the interlayer couplings of the bilayer CrI₃ can significantly reduce the interfacial sliding energy barriers and thus contribute to ZNDF. Moreover, phase transition between the in-plane (p_x and p_y) and out-of-plane (p_z) wave-functions dominates the sliding barrier evolutions, which is attributed to the delicate interplays among the interlayer vdW, electrostatic interactions, and the intralayer deformation of the CrI₃ layers under external load. The present findings may motivate a new concept of slide-spintronics and are expected to play an instrumental role in design of novel magnetic solid lubricants applied in various spintronic nano-devices.