Experimental realization of topological corner states in long-range-coupled electrical circuits

Topological corner states are zero-dimensional localized excitations whose existence is protected by the bulk properties of the system. This feature makes them robust to disorder unveiling intriguing physics. Canonical realizations of higher-order topology in two-dimensional systems typically rely on tight-binding models with the nearest-neighbor couplings. Here, in contrast, we propose a D-4-symmetric system where the topological band gap opens due to the additional long-range interactions, which are controllably incorporated in our setup based on a resonant electrical circuit. In our experiments, we probe the response of the designed circuit at every node, reconstruct the eigenmode profiles, and directly extract the topological invariant demonstrating the topological origin of the observed symmetry-protected corner states.