Following the discovery of moiré-driven superconductivity and density waves in twisted-graphene multilayers, twistronics has spurred a surge of interest in tailored broken symmetries through angular rotations enabling new properties, from electronics to photonics and phononics. Analogously, in monoclinic polar crystals a nontrivial angle between nondegenerate dipolar phonon resonances can naturally emerge due to asymmetries in their crystal lattice, and its variations are associated with intriguing polaritonic phenomena, including axial dispersion, i.e., the rotation of the optical axis with frequency, and microscopic shear effects that result in an asymmetric distribution of material loss. So far, these phenomena have been restricted to specific midinfrared frequencies difficult to access with conventional laser sources and fundamentally limited by the degree of asymmetry and by the strength of light-matter interactions available in natural crystals. Here, we leverage the twistronics concept to demonstrate maximal axial dispersion and loss redistribution of hyperbolic waves in elastic metasurfaces, achieved by tailoring the angle between coupled metasurface pairs featuring tailored anisotropy. We show extreme control over elastic wave dispersion and absorption via the twist angle and leverage the resulting phenomena to demonstrate enhanced propagation distance, in-plane reflection-free negative refraction and diffraction-free defect detection. Our work welds the concepts of twistronics, non-Hermiticity, and extreme anisotropy, demonstrating the powerful opportunities enabled by metasurfaces for tunable, highly directional surface-acoustic-wave propagation of great interest for a wide range of applications spanning from seismic mitigation to on-chip phononics and wireless communication systems, hence paving the way toward their translation into emerging photonic and polaritonic metasurface technologies.

中文翻译：

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扭转诱导双曲剪切超表面


随着在扭曲石墨烯多层中发现莫尔驱动的超导性和密度波，扭曲电子学激发了人们对通过角度旋转定制破缺对称性的兴趣，从而实现从电子学到光子学和声学的新特性。类似地，在单斜极性晶体中，由于其晶格的不对称性，非简并偶极声子共振之间的非平凡角度可以自然地出现，并且其变化与有趣的极化现象相关，包括轴向色散，即光轴随频率的旋转，和微观剪切效应导致材料损失的不对称分布。到目前为止，这些现象仅限于传统激光源难以达到的特定中红外频率，并且从根本上受到不对称程度和天然晶体中光与物质相互作用强度的限制。在这里，我们利用扭转电子学概念来演示弹性超表面中双曲波的最大轴向色散和损耗重新分布，这是通过定制具有定制各向异性的耦合超表面对之间的角度来实现的。我们通过扭转角展示了对弹性波色散和吸收的极端控制，并利用由此产生的现象来证明增强的传播距离、面内无反射负折射和无衍射缺陷检测。 我们的工作融合了扭转电子学、非厄米性和极端各向异性的概念，展示了超表面为可调谐、高度定向的表面声波传播带来的强大机会，这对于从地震缓解到现场监测等广泛应用产生了极大的兴趣。芯片声学和无线通信系统，从而为它们转化为新兴的光子和极化子超表面技术铺平了道路。