Topological waves guided by a glide-reflection symmetric crystal interface

Abstract: A domain wall separating two different topological phases of the same crystal can support the propagation of backscattering-immune guided waves. In valley-Hall and quantum-Hall crystal waveguides, this property stems from symmetry protection and results from a topological transition at a Dirac point. Since an initially closed band gap has to open, the guidance bandwidth remains limited compared to that of wide band gap crystals. When a glide-symmetric dislocation is introduced in a 2D crystal, we show that a pair of wide-bandwidth, single-mode, and symmetry-protected guided waves appear in the bulk band gap. The 2D Zak phase changes by $\pi$ on either side of the interface, providing a topological invariant protected by glide-reflection symmetry at the X point of the Brillouin zone. A demonstration experiment is performed with acoustic waves in water, at ultrasonic frequencies, and shows the continuous tuning of transmission as a function of the glide parameter. The concept further extends to other types of waves, including the case of elastic waves in solids, but also of optical and electromagnetic waves.