Fig. 3: Observation of multiple gapless edge modes.
a Distribution of the Berry curvature in the 2D Brillouin zone of the lower band in the tight-binding model, full-wave simulation, and experiment, from left to right. The lower and upper halves of the Brillouin zone have opposite Berry curvatures, leading to sub-Brillouin zone Chern numbers of  −1 and  +1, respectively. b Plot of eigenfrequencies for finite-size acoustic crystals with different θ. The gray dots denote bulk modes, while the red and blue dots correspond to edge modes at the left and right edges, respectively. Measured acoustic intensities at the c left and d right edges. The source and probe are placed in the same outermost resonator in the measurement.
