Fig. 3.

Unidirectional waveguide modes in experiment. (A) A single edge gyroscope is excited for five periods; subsequent images show the excitation propagation clockwise around the edge. The bottom graph indicates the displacement of one gyroscope (indicated with a triangle) in the y direction; the excitation is seen to persist for many cycles around the edge. (B) The same experiment as in A, but with three gyroscopes removed from the bottom edge and replaced with fixed magnets (to keep the system in equilibrium). Owing to the topological nature of the edge modes, the excitation propagates around the disturbance.