  Superlubricity, or alternatively termed structural (super)lubrictiy, is a
concept where ultra-low friction is expected at the interface between sliding
surfaces if these surfaces are incommensurate and thus unable to interlock. In
this work, we now report on sudden, reversible, friction changes that have been
observed during AFM based nanomanipulation experiments of gold nanoparticles
sliding on highly oriented pyrolythic graphite. These effects are can be
explained by rotations of the gold nanoparticles within the concept of
structural superlubricity, where the occurrence of ultra-low friction can
depend extremely sensitively on the relative orientation between the slider and
the substrate. From our theoretical simulations it will become apparent how
even miniscule magnitudes of rotation are compatible to the observed effects
and how size and shape of the particles can influence the dependence between
friction and relative orientation.
