  Impurity-induced defects play a crucial role for the properties of crystals,
but little is known about impurities with anisotropic shape. Here, we study how
colloidal dumbbells distort and interact with a hexagonal crystal of charged
colloidal spheres at a fluid interface. We find that subtle changes in the
dumbbell length induce a transition from a local distortion to a particle-bound
dislocation, and determine how the dumbbell moves inside the repulsive
hexagonal lattice. Our results provide new routes towards controlling material
properties through particle-bound dislocations.
