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.

中文翻译：

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二维空间中具有全被动声奇偶时间对称超材料晶体的单向波矢量操纵

探索非厄密哈密顿量与经典波系统有关的奇偶时间对称性的概念引起了极大的兴趣，因为它可以通过量子经典模拟对奇偶时间对称系统进行实验研究。在这里，我们演示了在二维空间中使用全无源声学奇偶时间对称超材料晶体的单向波矢量操纵。超材料晶体是通过交织凹槽和孔结构的声学超材料而构造的，以提供二维扩展且弯曲的固有奇偶时间对称电势，从而可以灵活地操纵不成对的波矢量。在从不间断到奇偶时间对称阶段的过渡点，在频谱上通过实验实现了单向声聚焦效果（以及相反方向的无反射声透明效果）。该演示证实了无源声学系统具有进行一般奇偶时间对称物理实验研究的能力，并进一步揭示了通过精心定制的空间单向波矢量实现的独特功能。