Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China.
School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China.
Phys Rev Lett. 2018 Mar 23;120(12):124502. doi: 10.1103/PhysRevLett.120.124502.
Exploring the concept of non-Hermitian Hamiltonians respecting parity-time symmetry with classical wave systems is of great interest as it enables the experimental investigation of parity-time-symmetric systems through the quantum-classical analogue. Here, we demonstrate unidirectional wave vector manipulation in two-dimensional space, with an all passive acoustic parity-time-symmetric metamaterials crystal. The metamaterials crystal is constructed through interleaving groove- and holey-structured acoustic metamaterials to provide an intrinsic parity-time-symmetric potential that is two-dimensionally extended and curved, which allows the flexible manipulation of unpaired wave vectors. At the transition point from the unbroken to broken parity-time symmetry phase, the unidirectional sound focusing effect (along with reflectionless acoustic transparency in the opposite direction) is experimentally realized over the spectrum. This demonstration confirms the capability of passive acoustic systems to carry the experimental studies on general parity-time symmetry physics and further reveals the unique functionalities enabled by the judiciously tailored unidirectional wave vectors in space.
探索具有奇偶时间对称性的非厄米哈密顿量的概念对于经典波系统具有重要意义，因为它可以通过量子-经典模拟来实验研究奇偶时间对称系统。在这里，我们通过全被动声学奇偶时间对称超材料晶体演示了二维空间中的单向波矢操控。该超材料晶体通过交错槽状和孔状声学超材料构建，提供了二维扩展和弯曲的固有奇偶时间对称势，从而实现了非配对波矢的灵活操控。在从不破缺的奇偶时间对称相到破缺的奇偶时间对称相的转变点，在整个频谱范围内实验实现了单向声聚焦效应（同时在相反方向实现无反射声透明性）。该演示证实了被动声系统在进行一般奇偶时间对称物理实验研究方面的能力，并进一步揭示了通过在空间中巧妙地调整单向波矢所实现的独特功能。
