▎ 摘　　要

According to the classic law of Da Vinci-Amontons, a friction force f was found to increase macroscopically with an external normal load N(f = mu N), with a positive definite friction coefficient mu. Here we employ first -principles calculations to predict that, when sliding the ferroelectric two-dimensional In2Se3 over graphene, the differential friction coefficient mu, measured by the slope of the corrugation in the sliding potential energy barrier subject to load N, displays an overall positive feather when the dipole is aligned toward the In2Se3 -graphene interface; however, mu exhibits intriguing negative-positive oscillation with increasing N when the dipole is aligned outward from the interface. Such striking observations can be rationalized by the van der Waals and electrostatic interaction-induced competition between the downward shift of the sliding barrier by the p(x)- and p(y)-like levels and the upward shift of the barrier by the p(z) states, which is accompanied by an oscillation of the In2Se3-graphene interfacial charge redistribution subject to the external load. The present findings are expected to play an instrumental role in the design of high-performance solid lubricants.