Measurement of Corner-Mode Coupling in Acoustic Higher-Order Topological Insulators

Recent developments of band topology have revealed a variety of higher-order topological insulators (HOTIs). These HOTIs are characterized by a variety of different topological invariants, making them different at a fundamental level. However, despite such differences, the fact that they all sustain higher-order topological boundary modes poses a challenge to phenomenologically tell them apart. This work presents experimental measurements of the coupling effects of topological corner modes (TCMs) existing in two different types of two-dimensional acoustic HOTIs. Although both HOTIs have a similar four-site square lattice, the difference in magnetic flux per unit cell dictates that they belong to different types of topologically nontrivial phases-one lattice possesses quantized dipole moments, but the other is characterized by quantized quadrupole moment. A link between the topological invariants and the response line shape of the coupled TCMs is theoretically established and experimentally confirmed. Our results offer a pathway to distinguish HOTIs experimentally.

Automated summary

Experimental measurements were conducted on coupling effects of topological corner modes (TCMs) in two different types of two-dimensional acoustic HOTIs, revealing differences in their topological invariants and response line shapes. A theoretical link between the topological invariants and the coupled TCMs' response line shape was established and experimentally confirmed, providing a pathway to distinguish HOTIs experimentally.