Topological phononic insulator with robustly pseudospin-dependent transport

TL;DR

This paper demonstrates a topological phononic insulator with pseudospin-dependent transport, enabling reconfigurable, robust acoustic waveguides immune to defects, achieved through a topological phase transition in rotatable triangular phononic crystals.

Contribution

It introduces a new method to realize topological phase transition in phononic crystals with C3v symmetry and demonstrates reconfigurable, robust sound transport along topological domain walls.

Findings

Experimental observation of quantum spin Hall effect for sound.

Reconfigurable acoustic pathways via crystal rotation.

Robust one-way edge transport immune to defects.

Abstract

Topological phononic states, facilitating acoustic unique transports immunizing to defects and disorders, have significantly revolutionized our scientific cognition of acoustic wave systems. Up to now, the theoretical and experimental demonstrations of topologically protected one-way transports with pseudospin states in a phononic crystal beyond the graphene lattice with C6v symmetry are still unexploited. Furthermore, the tunable topological states, in form of robust reconfigurable acoustic pathways, have been evaded in the topological phononic insulators. Here, we realize a topological phase transition in the double Dirac degenerate cone of rotatable triangular phononic crystals with C3v symmetry, by introducing the zone folding mechanism. Along a topological domain wall between two portions of phononic crystals with distinct topological phases, we experimentally observe the quantum spin Hall (QSH) effect for sound, characterized by the robust pseudospin-dependent one-way edge model. As the triangular phononic crystals can freely rotate, we straightforward reconfigure an arbitrary contour defined by the topological domain wall along which the acoustic waves can unimpededly transport. Our research develops a new route for the exploration of the topological phenomena in experiments and provides an excellent framework for freely steering the acoustic immune-backscattering propagation within topological phononic structures.