  Negative friction coefficients, where friction is reduced upon increasing
normal load, are predicted for superlubric graphite-hexagonal boron nitride
heterojunctions. The origin of this counterintuitive behavior lies in the
load-induced suppression of the moir\'e superstructure out-of-plane distortions
leading to a less dissipative interfacial dynamics. Thermally induced
enhancement of the out-of-plane fluctuations leads to an unusual increase of
friction with temperature. The highlighted frictional mechanism is of a general
nature and is expected to appear in many layered material heterojunctions.
