Synthetic gauge flux and Weyl points in acoustic systems

Realizing non-trivial topological effects is challenging in acoustic systems. It is now shown that inversion symmetry breaking can be used to create acoustic analogues of the topological Haldane model. Following the discovery of the quantum Hall effect 1 , 2 and topological insulators 3 , 4 , the topological properties of classical waves began to draw attention 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 . Topologically non-trivial bands characterized by non-zero Chern numbers are realized through either the breaking of time-reversal symmetry using an external magnetic field 5 , 6 , 7 , 15 , 16 or dynamic modulation 8 , 17 . Owing to the absence of a Faraday-like effect, the breaking of time-reversal symmetry in an acoustic system is commonly realized with moving background fluids 20 , 22 , which drastically increases the engineering complexity. Here we show that we can realize effective inversion symmetry breaking and create an effective gauge flux in a reduced two-dimensional system by engineering interlayer couplings, achieving an acoustic analogue of the topological Haldane model 2 , 23 . We show that the synthetic gauge flux is closely related to Weyl points 24 , 25 , 26 in the three-dimensional band structure and the system supports chiral edge states for fixed values of k z .