Acoustic spin-Chern insulator induced by synthetic spin-orbit coupling with spin conservation breaking

TL;DR

This paper demonstrates a 2D acoustic crystal that mimics spin-orbit coupling, creating topologically protected helical boundary states and enabling tunable transport paths, advancing acoustic topological insulators without magnetic fields.

Contribution

It introduces a novel acoustic crystal design that simulates spin-orbit coupling and topological insulator behavior without symmetry constraints or magnetic fields.

Findings

Experimental observation of gapless, helical boundary states.

Tunable transport paths via geometric adjustments.

Realization of acoustic topological insulator with synthetic spin-orbit coupling.

Abstract

Topologically protected surface modes of classical waves hold the promise to enable a variety of applications ranging from robust transport of energy to reliable information processing networks. The integer quantum Hall effect has delivered on that promise in the electronic realm through high-precision metrology devices. However, both the route of implementing an analogue of the quantum Hall effect as well as the quantum spin Hall effect are obstructed for acoustics by the requirement of a magnetic field, or the presence of fermionic quantum statistics, respectively. Here, we use a two-dimensional acoustic crystal with two layers to mimic spin-orbit coupling, a crucial ingredient of topological insulators. In particular, our setup allows us to free ourselves of symmetry constraints as we rely on the concept of a non-vanishing "spin" Chern number. We experimentally characterize the emerging boundary states which we show to be gapless and helical. Moreover, in an H-shaped device we demonstrate how the transport path can be selected by tuning the geometry, enabling the construction of complex networks.