From daily intuitions to sophisticated atomic-scale experiments, friction is
usually found to increase with normal load. Using first-principle calculations, here we show
that the sliding friction of a graphene/graphene system can decrease with increasing normal
load and collapse to nearly zero at a critical point. The unusual collapse of friction is attributed
to an abnormal transition of the sliding potential energy surface from corrugated, to
substantially flattened, and eventually to counter-corrugated states. The energy dissipation
during the mutual sliding is thus suppressed sufficiently under the critical pressure. The friction
collapse behavior is reproducible for other sliding systems, such as Xe/Cu, Pd/graphite, and
MoS2/MoS2, suggesting its universality. The proposed mechanism for diminishing energy
corrugation under critical normal load, added to the traditional structural lubricity, enriches our fundamental understanding
about superlubricity and isostructural phase transitions and offers a novel means of achieving nearly frictionless sliding interfaces.