Observation of Higher-Dimensional Point-Gap Bulk-Boundary Correspondence

The bulk-boundary correspondence (BBC), a cornerstone of topological physics that links bulk topology to boundary response, has long been established within the framework of line-gap topology. Recently, the BBC concept has been extended to non-Hermitian point gaps, addressing a crucial gap in our understanding of topological phases. Here, we report the first observation of higher-dimensional point-gap BBC using our versatile acoustic platform. We implement a compact two-dimensional point-gap topological insulator characterized by a nontrivial open-bulk Chern number, whose spectrum maps intuitively onto a momentum-resolved Su-Schrieffer-Heeger model. Experimentally, we directly visualize the iconic point-gap spectrum characteristic via a mixed-dimensional acoustic setup (one real-space, one synthetic-momentum). Most notably, using two real two-dimensional samples with distinct boundary conditions, we observe topological edge states and the bipolar non-Hermitian skin effect, respectively. Together, these complementary observations constitute decisive evidence for the point-gap BBC and complete a crucial missing pillar in non-Hermitian topological physics.