Abstract
The quantum Hall effect (QHE) associated with Chern insulators reveals the non-trivial topological properties of two-dimensional electronic systems subject to strong magnetic field, which features finite Chern number C and chiral edge states. The latter promise robust electron transport and have received tremendous attention in both the condensed matter physics and classical systems including photonics and acoustics. In acoustics, circulating air flow has been introduced to create an effective gauge magnetic field, which breaks the time-reversal symmetry and leads to chiral edge states for acoustic waves. While the robust edge states may offer possible routes towards acoustic devices yielding unidirectional sound propagation, e.g., acoustic diodes, the mode density at the interfaces is limited by small Chern numbers of ±1. Here, we realize acoustic Chern insulators with large Chern numbers, i.e., |C|≥ 1 (|C| = 1, 2, 3, 4). The system is based on circulating air flow in a sonic crystal (SC) with fourfold rotational symmetry. The large Chern numbers are obtained by breaking multiple accidental degeneracies at (non-)high-symmetric points. Based on these Chern insulators, acoustic diodes are realized by joining structures of different Chern numbers. Up to eight propagation modes are supported on the interfaces, greatly improving the mode density and hence the propagation efficiency. Our design offers possible routes towards high-efficient and topologically robust acoustic diodes, which may further inspire acoustic non-reciprocal devices based on topological Chern insulators. Experimentally, our proposals can be realized based on angular-momentum-biased resonator arrays.
Highlights
The concept of topology has generated great research interest in the last few decades [1,2,3,4,5,6,7,8,9,10]
It was proposed that circulating air flow can act as an equivalent magnetic field for sound and provides an effective technique to break the timereversal symmetry in acoustics [37]
We have realized acoustic Chern insulators with large Chern numbers in sonic crystal (SC) based on circulating air flow
Summary
The concept of topology has generated great research interest in the last few decades [1,2,3,4,5,6,7,8,9,10]. It was proposed that circulating air flow can act as an equivalent magnetic field for sound and provides an effective technique to break the timereversal symmetry in acoustics [37]. By using this technique, acoustic Chen insulators are realized, as an analogy of the QHE, supporting robust and unidirectional interface states for sound [27, 28, 30, 31]. Based on these Chern insulators, acoustic diodes with large mode density are realized by joining structures of different Chern numbers, forming a diode network, where up to eight unidirectional sound “roadways” are obtained for each diode channel
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