  In our combined experimental, theoretical and numerical work, we study the
out of equilibrium deformations in a shrinking ring of optically trapped,
interacting colloidal particles. Steerable optical tweezers are used to confine
dielectric microparticles along a circle of discrete harmonic potential wells,
and to reduce the ring radius at a controlled quench speed. We show that
excluded-volume interactions are enough to induce particle sliding from their
equilibrium positions and nonequilibrium zigzag roughening of the colloidal
structure. Our work unveils the underlying mechanism of interfacial deformation
in radially driven microscopic discrete rings.
