Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama 351-0198, Japan.
Nonlinear Physics Centre, RSPE, The Australian National University, Canberra, ACT 0200, Australia.
Phys Rev Lett. 2019 Aug 2;123(5):054301. doi: 10.1103/PhysRevLett.123.054301.
Recently, it was shown that surface electromagnetic waves at interfaces between continuous homogeneous media (e.g., surface plasmon-polaritons at metal-dielectric interfaces) have a topological origin [K. Y. Bliokh et al., Nat. Commun. 10, 580 (2019)NCAOBW2041-172310.1038/s41467-019-08397-6]. This is explained by the nontrivial topology of the non-Hermitian photon helicity operator in the Weyl-like representation of Maxwell equations. Here we analyze another type of classical waves: longitudinal acoustic waves corresponding to spinless phonons. We show that surface acoustic waves, which appear at interfaces between media with opposite-sign densities, can be explained by similar topological features and the bulk-boundary correspondence. However, in contrast to photons, the topological properties of sound waves originate from the non-Hermitian four-momentum operator in the Klein-Gordon representation of acoustic fields.
最近，人们已经证明了连续均匀介质界面上的表面电磁波（例如，金属-电介质界面上的表面等离激元）具有拓扑起源[K. Y. Bliokh 等人，Nat. Commun. 10, 580 (2019)NCAOBW2041-172310.1038/s41467-019-08397-6]。这可以通过麦克斯韦方程组的 Weyl 类似表示中的非厄米光子螺旋度算符的非平凡拓扑来解释。在这里，我们分析了另一种类型的经典波：与无自旋声子对应的纵声学波。我们表明，在密度符号相反的介质界面上出现的表面声波，可以用类似的拓扑特征和体边界对应关系来解释。然而，与光子不同的是，声波的拓扑性质来源于 Klein-Gordon 表示的声学场中的非厄米四动量算子。
