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中国物理学会期刊

一维非互易声学晶体的非厄米趋肤态操控

CSTR: 32037.14.aps.73.20241087

Steering non-Hermitian skin states by engineering interface in 1D nonreciprocal acoustic crystal

CSTR: 32037.14.aps.73.20241087
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  • 近年来, 基于非厄米拓扑理论, 研究者们通过调制声学晶体中的非互易耦合, 揭示了体态向界面塌陷的趋肤效应. 本工作实验设计了具有不同绕组数域之间的拓扑趋肤界面, 以操纵能量聚焦到非厄米一维声腔链的中间或两端. 首先, 通过电声耦合的方法实现了两个声学腔之间的非互易耦合, 并研究其特性. 其次, 将非互易耦合腔扩展成链状, 通过调制非互易电-声耦合来构建趋肤界面的位置. 实验结果表明, 对于不同的非互易耦合分布, 声音可以集中在中间界面或两端界面, 并且通过改变非互易耦合方向, 可以将趋肤界面从中间切换到两端. 本研究结果为设计控制声音传播的先进拓扑声学装置提供了一个新平台.

     

    Topological insulators possess strong topological protection properties and can manipulate the wave propagation to combat disorder and defects. And now they have grown into a large research field in photonic and phononic crystals. However, the conventional topological band theory is used to describe a closed photonic/phononic crystal that is assumed to be a Hermitian system. In fact, actual physical systems often couple with external environment, and generate non-Hermitian Hamiltonians with complex eigenvalues. Recently, many novel topological properties have been induced by the interaction between non-Hermitian phase and topological phase. A prominent example is non-Hermitian skin effect that all eigenstates are localized to the boundary in open system, which is different from the conventional topological edge state. This unique physical phenomenon has inspired various applications, such as wave funneling, enhanced sensing, and topological lasing. In this work, we describe the non-Hermitian skin effect by using winding number domains. The sign of the winding number domain determines the rotation direction of the loops in the complex frequency plane, whose sign can be controlled by the nonreciprocal coupling direction. In this work, we design different topological skin interfaces between different domains with opposite winding numbers to manipulate the energy focusing on middle or two-end of non-Hermitian one-dimensional acoustic cavity chain. In experiment, we use an electroacoustic coupling method, in which a unidirectional coupler composed of microphones, speakers, phase shifters, and amplifiers is used to introduce positive and negative non-reciprocal couplings between the two acoustic cavities, and study the characteristics of these non-reciprocal couplings. Then, the non-reciprocal coupling cavities are extended into a chain structure, and the magnitudes and signs of the non-reciprocal couplings are flexibly controlled by using phase shifters and amplifiers. Through this method, we successfully construct the interfaces between different winding number domains, achieving a one-dimensional non-Hermitian skin effect at various interfaces. The experimental results indicate that the sound can be focused on the middle interface or two-end interfaces for different nonreciprocal coupling distributions, and the skin interface can also be switched from middle to two-end by exchanging the nonreciprocal coupling direction of the domains. Our research results provide greater flexibility for designing acoustic devices and also a new platform for exploring advanced topological acoustic systems for controlling sound propagation.

     

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