声子晶体中四重简并狄拉克节线半金属及其非常规表面响应的观测
Observation of fourfold Dirac nodal line semimetal and its unconventional surface responses in sonic crystals
AI总结：
本文首次在声子晶体中实验观测到四重简并狄拉克节线半金属，揭示其Berry相位为2π并导致环面表面态或完全无表面态等非常规表面响应，为声表面波灵活操控开辟新方向。
摘要：
三维节线半金属（NLSMs）对于丰富拓扑物理和波动调控都具有重要意义。然而，在声学系统中实现的NLSMs通常是二重简并的能带，被称为Weyl NLSMs。在此，我们首次报道了在声子晶体中实验观测到具有四重简并的新型Dirac NLSMs。我们揭示了Dirac NLSMs的拓扑性质与传统Weyl NLSMs完全不同。与狄拉克节线（DNL）相关的Berry相位为2π，这导致Dirac NLSMs的表面响应呈现两种截然不同的情形：一个占据整个表面布里渊区（SBZ）的环面表面态，以及SBZ中不存在任何表面态。我们进一步揭示了由DNL引起的拓扑表面弧可以从开放轮廓变为闭合轮廓。Dirac NLSMs及其独特表面响应的发现可能为声表面波的灵活操控开辟令人振奋的新前沿。
英文摘要：
Three-dimensional nodal line semimetals (NLSMs) provide remarkable importance for both enrich topological physics and wave management. However, NLSMs realized in acoustic systems are twofold bands degenerate, which are called Weyl NLSMs. Here, we first report on the experimental observation of novel Dirac NLSMs with fourfold degenerate in sonic crystals. We reveal that the topological properties of the Dirac NLSMs are entirely different than that of the conventional Weyl NLSMs. The Berry phase related to the Dirac nodal line (DNL) is 2π, which results in the surface responses of the Dirac NLSMs with two radically different situations: a torus surface state occupying the entire surface Brillouin zone (SBZ) and without any surface state in the SBZ. We further reveal that topological surface arcs caused by DNL can change from open to closed contours. The findings of Dirac NLSMs and their unique surface response may provoke exciting frontiers for flexible manipulation of acoustic surface waves.
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