Higher-order Skin Effect through a Hermitian-non-Hermitian Correspondence and Its Observation in an Acoustic Kagome Lattice

TL;DR

This paper predicts and experimentally demonstrates the higher-order non-Hermitian skin effect in an acoustic Kagome lattice, showing energy localization at a corner due to topological properties, using a Hermitian-non-Hermitian correspondence.

Contribution

It introduces a novel approach linking Hermitian and non-Hermitian systems to observe higher-order NHSE in acoustic lattices, with experimental validation.

Findings

Energy localizes at a corner in the topologically nontrivial phase.

Energy spreads out at frequencies of bulk states.

Experimental observation confirms the higher-order NHSE.

Abstract

The non-Hermitian skin effect (NHSE) is a distinctive topological phenomenon observed in nonHermitian systems. Recently, there has been considerable interest in exploring higher-order NHSE occurrences in two and three dimensions. In such systems, topological edge states collapse into a corner while bulk states remain delocalized. Through a Hermitian-non-Hermitian correspondence, this study predicts and experimentally observes the higher-order NHSE in an acoustic Kagome lattice possessing nonreciprocal hoppings. By rotating the frequency spectrum and employing complexfrequency excitation techniques, we observe the localization of acoustic energy towards a corner of the lattice in the topologically nontrivial phase, even when the source is located far from that corner. In contrast, the acoustic energy spreads out when excited at the frequencies hosting the bulk states. These observations are unequivocal evidence of the higher-order NHSE.