  Friction in ordered atomistic layers plays a central role in various
nanoscale systems ranging from nanomachines to biological systems. It governs
transport properties, wear and dissipation. Defects and incommensurate lattice
constants dramatically change these properties. Recently experimental systems
have become accessible to probe the dynamics of nanofriction. Here, we present
a model system consisting of laser-cooled ions in which nanofriction and
transport processes in self-organized systems with back action can be studied
with atomic resolution. We show that in a system with local defects resulting
in incommensurate layers, there is a transition from sticking to sliding with
Aubry-type signatures. We demonstrate spectroscopic measurements of the soft
vibrational mode driving this transition and a measurement of the order
parameter. We show numerically that both exhibit critical scaling near the
transition point. Our studies demonstrate a simple, well-controlled system in
which friction in self-organized structures can be studied from classical- to
quantum-regimes.
