  Little is known about the quantum effects of friction, and first-principles
studies are virtually non-existent. In multilayer graphene, the order of the
stacking of the layers plays a crucial role in the electronic properties and
the manifestation of superconductivity, and friction affects how layers slide
to change the stacking. Here, we study the effects of friction in bilayer
graphene by focusing on quantum fluctuations in the free energy barrier that
layers have to overcome to slide with respect to each other. We evaluate the
free energy at the barrier in bilayer graphene through the self-consistent
harmonic approximation, accounting for quantum and thermal ionic fluctuations.
We obtain a very large reduction of the barrier of more than 30%. Temperature
effects are weaker, although high temperatures induce a significant reduction
of the barrier as well. Our approach is general and paves the way for
systematically accounting for nuclear quantum and thermal effects in free
energy barriers of other macroscopic systems.
