Topologically protected waves in classical media provide unique opportunities for one-way wave transport and immunity to defects. Contrary to acoustics and electromagnetics, their observation in elastic solids has so far been elusive because of the presence of multiple modes and their tendency to hybridize at interfaces. Here, we report on the experimental investigation of topologically protected helical edge modes in elastic plates patterned with an array of triangular holes, along with circular holes that produce an accidental degeneracy of two Dirac cones. Such a degeneracy is subsequently lifted by careful breaking of the symmetry along the thickness direction, which emulates the spin orbital coupling in the quantum spin Hall effect. The joining of two plates that are mirror-symmetric copies of each other about the plate midthickness introduces a nontrivial interface that supports helical edge waves. The experimental observation of these topologically protected wave modes in elastic continuous plates opens avenues for the practical realization of structural components with topologically nontrivial waveguiding properties and their application to elastic waveguiding and confinement.

中文翻译：

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图案化弹性板中拓扑保护的螺旋边缘模式的实验观察

经典介质中受拓扑保护的波浪为单向波浪传输和抗缺陷提供了独特的机会。与声学和电磁学相反，由于存在多种模式以及它们在界面处发生杂交的趋势，因此迄今为止在弹性固体中的观察还难以捉摸。在这里，我们报告的实验研究了弹性板中的拓扑受保护的螺旋边缘模式，该弹性板具有一系列三角形孔，以及产生两个Dirac锥的意外简并的圆形孔。随后通过沿厚度方向小心地打破对称性来消除这种简并性，这模仿了量子自旋霍尔效应中的自旋轨道耦合。围绕板的中间厚度彼此镜像对称复制的两个板的接合引入了支撑螺旋边缘波的非平凡界面。对弹性连续板中这些受拓扑保护的波模式的实验观察为具有拓扑非平凡波导特性的结构部件的实际实现及其在弹性波导和约束中的应用开辟了道路。