  Although glassy relaxation is typically associated with disorder, here we
report on a new type of glassy dynamics relating to dislocations within 2-D
crystals of colloidal dimers. Previous studies have demonstrated that
dislocation motion in dimer crystals is restricted by certain particle
orientations. Here, we drag an optically trapped particle through such dimer
crystals, creating dislocations. We find a two-stage relaxation response where
initially dislocations glide until encountering particles that cage their
motion. Subsequent relaxation occurs logarithmically slowly through a second
process where dislocations hop between caged configurations. Finally, in
simulations of sheared dimer crystals, the dislocation mean squared
displacement displays a caging plateau typical of glassy dynamics. Together,
these results reveal a novel glassy system within a colloidal crystal.
