Experimental Demonstration of Acoustic Valley Hall Topological Insulators with the Robust Selection of C3v-Symmetric Scatterers

Topological insulators are a research hotspot due to their unique properties of backscattering immunity and defect insensitivity for edge states propagating on the complex boundaries. The analogues of valley states in electronic systems have recently led to acoustic valley Hall topological insulators. Acoustic valley edge states often exist on the domain walls between two phononic crystals that have different nonvanishing valley Chern indices, which are implemented by rotating the identical primitive unit cells. The restriction on using the same primitive unit cells in previous works does not show the realization of aperiodic valley topological insulators. We construct various configurations composed by two or more differently shaped primitive unit cells. Valley edge states are both numerically and experimentally demonstrated with the robust selection of C-3 nu-symmetric scatterers in adjacent domains. We also experimentally demonstrate the valley-selective cross-waveguide beam splitter by measuring the transmission spectra. The robust selection of C-3 nu-symmetric scatterers in this work may provide more possibilities for designing alternative acoustic-topological-insulator-based devices with flexible structures.