Experimental Realization of Weyl Exceptional Rings in a Synthetic Three-Dimensional Non-Hermitian Phononic Crystal

TL;DR

This paper demonstrates the experimental creation of Weyl exceptional rings in a 3D non-Hermitian phononic crystal, revealing new topological phenomena and Fermi arcs in acoustic systems with gain and loss.

Contribution

It introduces a novel experimental realization of Weyl exceptional rings in a synthetic 3D non-Hermitian phononic crystal, combining topological physics with acoustics.

Findings

Weyl exceptional rings observed in a 1D phononic crystal with gain and loss.

Fermi arcs persist despite non-Hermitian effects.

Topological charge and winding numbers characterize the WERs.

Abstract

Weyl points (WPs) are isolated degeneracies carrying quantized topological charges, and are therefore robust against Hermitian perturbations. WPs are predicted to spread to the Weyl exceptional rings (WERs) in the presence of non-Hermiticity. Here, we use a one-dimensional (1D) Aubry-Andre-Harper (AAH) model to construct a Weyl semimetal in a 3D parameter space comprised of one reciprocal dimension and two synthetic dimensions. The inclusion of non-Hermiticity in the form of gain and loss produces a WER. The topology of the WER is characterized by both its topological charge and non-Hermitian winding numbers. The WER is experimentally observed in a 1D phononic crystal with the non-Hermiticity introduced by active acoustic components. In addition, Fermi arcs are observed to survive the presence of non-Hermitian effect. We envision our findings to pave the way for studying the high-dimensional non-Hermitian topological physics in acoustics.