Observation of Anti-helical Edge States in Acoustic Metamaterials

TL;DR

This paper reports the first experimental observation of anti-helical edge modes in acoustic metamaterials, revealing new topological phases with copropagating edge states that could lead to innovative device designs.

Contribution

It introduces an acoustic implementation of anti-helical edge modes based on a bilayer model with staggered interlayer hoppings, expanding topological phase studies.

Findings

Experimental evidence of antiHEMs in acoustic platform

Identification of energy-biased Dirac points in bulk spectra

Selective excitation of spin subspaces

Abstract

As a hallmark of the quantum Hall effect, chiral edge modes (CEMs) counterpropagate along the two parallel edges of a ribbon structure. However, recent studies demonstrate counterintuitive antiCEMs that copropagate along the parallel edges. Analogous to the established extension of the CEMs to helical edge modes (HEMs) in the quantum spin Hall effect, it is natural to extend the antiCEMs to antiHEMs, which comprise a pair of time-reversal-related antiCEMs. In this Letter, we report the first observation of the antiHEMs based on a bilayer model that features staggered positive and negative interlayer hoppings. Experimentally, we implement this anti-helical model on an acoustic platform and provide compelling evidence for the antiHEMs by selectively exciting different spin subspaces, along with identifying the energybiased Dirac points in bulk spectra. Our findings may offer new insights into topological phases of matter and potentially pave the way for designing novel devices with unique edge transport properties.