Fig. 3: Experimental demonstration of an acoustic octupole topological insulator.
From: Observation of an acoustic octupole topological insulator
a Photo of the fabricated sample with five unit cells along each direction. The scale bar is 100 mm. b Left panel: measured sound intensity of all sites at an arbitrarily chosen frequency (2000 Hz). Right panel: illustration of the four regions (corner, hinge, surface and bulk) used to calculate the average intensity spectra. c Measured average intensity spectra for a finite lattice in the topological phase. d–g Spatial distributions of the acoustic response intensity, integrated over different sets of frequencies corresponding to the corner (d), hinge (e), surface (f) and bulk (g) spectra; the frequency ranges are indicated by the corresponding coloured regions in c.
