  The possibility to achieve entirely frictionless, i.e. superlubric, sliding
between solids, holds enormous potential for the operation of mechanical
devices. At small length scales, where mechanical contacts are well-defined,
Aubry predicted a transition from a superlubric to a pinned state when the
mechanical load is increased. Evidence for this intriguing Aubry transition
(AT), which should occur in one dimension (1D) and at zero temperature, was
recently obtained in few-atom chains. Here, we experimentally and theoretically
demonstrate the occurrence of the AT in an extended two-dimensional (2D) system
at room temperature using a colloidal monolayer on an optical lattice. Unlike
the continuous nature of the AT in 1D, we observe a first-order transition in
2D leading to a coexistence regime of pinned and unpinned areas. Our data
demonstrate that the original concept of Aubry does not only survive in 2D but
is relevant for the design of nanoscopic machines and devices at ambient
temperature.
