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

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. 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 construct a two-dimensional topological acoustic crystal induced by the synthetic spin-orbit coupling, a crucial ingredient of topological insulators, with spin non-conservation. Our setup allows us to free ourselves of symmetry constraints as we rely on the concept of a nonvanishing "spin" Chern number. We experimentally characterize the emerging boundary states which we show to be gapless and helical. More importantly, we observe the spin flipping transport in an H-shaped device, demonstrating evidently the spin non-conservation of the boundary states.

Synthetic Mechanical Lattices with Synthetic Interactions

“…Networks of coupled harmonic oscillators have long served as a foundational model for understanding thermal transport in solids [1], and over the past decade have additionally become a powerful theoretical and experimental platform for exploring topology [2] and its connections to mechanical structures [3][4][5]. While experiments based on physically coupled oscillators offer powerful capabilities for the realization of artificial materials and the visualization of novel transport phenomena therein [6][7][8][9][10][11][12][13][14][15][16][17][18], such physical coupling terms present natural limitations on the Hamiltonians that may be directly engineered. For example, Newton's third law dictates that the direct hopping terms should obey reciprocity, with forward and backward tunneling pathways having equal amplitudes.…”

Tunable Topological Surface States of Three-Dimensional Acoustic Crystals

“…The advantages of classical-wave systems in studying topological behaviors come from their flexible structures, less complicated samples, and more accessible measurements [9][10][11][12]. Since then, there have been enormous works focusing on the classical-wave analogs of topological phases, ranging from one-dimensional (1D) to threedimensional (3D) and even higher synthetic dimensions [13][14][15][16][17][18][19][20][21][22]. These topological models provide unprecedented ways to manipulate waves with robust and symmetry-protected manners.…”

A General Method to Design Acoustic Higher-Order Topological Insulators

“…Originating from the condensed matter physics, the concept of topological insulators (TIs) [1-3] have been intensely investigated in the classical wave systems [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. More recently, as a counterpart of topological insulators in solid materials, the topological crystalline insulators (TCIs) that can host higher-order topological states have attracted growing attention [23][24][25][26][27].…”