Split-ring resonator coupling-induced tunable acoustic second-order topological insulators

The recent higher-order topological insulators (HOTIs) encoded with the tight-binding model (TBM) have been demonstrated beyond traditional bulk-edge correspondence, which shows the exotic capability of sound manipulation. However, the current waveguide resonator model with weak tunability in hopping controls has been used as the most common method to construct the TBM directly in a realistic acoustic system. Here, we present another carrier and methodology to realize the TBM based on split-ring resonators (SRRs) coupling in a realistic physical platform and construct a second-order topological insulator (SOTI) based on it, where the hopping and frequencies of the topological corner states can be easily tuned by adjusting the coupling strength of the SRRs. Numerical analysis and experimental measurement demonstrated zero-dimensional topological corner states in this acoustic resonant system. The findings provide a more flexible method for tunable acoustic HOTIs realization.