Experimental evidence of robust acoustic valley Hall edge states in a non-resonant topological elastic waveguide

TL;DR

This study provides experimental validation of robust acoustic valley Hall edge states in a non-resonant elastic waveguide, demonstrating effective propagation, suppressed backscattering, and selective mode excitation due to weak valley coupling.

Contribution

It introduces a non-resonant elastic waveguide design that breaks space inversion symmetry without resonant units, experimentally confirming topological edge states and their properties.

Findings

Edge modes propagate effectively along domain walls.

Disorder-induced backscattering is substantially suppressed.

Weak valley coupling enables selective mode excitation.

Abstract

This paper presents experimental evidence of the existence of acoustic valley Hall (AVHE) edge states in topological elastic waveguides. The fundamental lattice is assembled based on a non-resonant unit where space inversion symmetry (SIS) is broken by simply perturbing the underlying lattice geometry. This aspect is in net contrast with existing elastic AVHE designs that exploit locally-resonant units and require the addition of masses in order to break SIS. The experimental results presented in this study validate findings so far presented only at theoretical and numerical level. In particular, it is found that edge modes can effectively propagate along domain walls between topologically dissimilar domains and that disorder-induced backscattering is substantially suppressed due to the weak coupling between oppositely valley-polarized modes. The coupling between valley modes is also further investigated and linked to an evident chiral flux of the mechanical energy. Finally, we show that the weak coupling between the valleys can be exploited to achieve selective mode injection at the domain wall, hence realizing a very effective excitation strategy of the chiral edge states.