Acoustic Higher-Order Weyl Semimetal with Bound Hinge States in the Continuum

Abstract

Higher-order topological phases have raised widespread interest in recent years with the occurrence of the topological boundary states of dimension two or more less than that of the system bulk. The higher-order topological states have been verified in gapped phases, in a wide variety of systems, such as photonic and acoustic systems, and recently also observed in gapless semimetal phase, such as Weyl and Dirac phases, in systems alike. The higher-order topology is signaled by the hinge states emerging in the common bandgaps of the bulk states and the surface states. In this Letter, we report our first prediction and observation of a new type of hinge states, the bound hinge states in the continuum (BHICs) bulk band, in a higher-order Weyl semimetal implemented in phononic crystal. In contrast to the hinge state in gap, which is characterized by the bulk polarization, the BHIC is identified by the nontrivial surface polarization. The finding of the topological BHICs broadens our insight to the topological states, and may stimulate similar researches in other systems such as electronic, photonic, and cold atoms systems. Our work may pave the way toward high-Q acoustic devices in application.

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• Engineering second-order topological insulators via coupling two first-order topological insulators
• Higher-order Klein bottle topological insulator in three-dimensional acoustic crystals
• Observation of Dual-band Topological Corner Modes in Acoustic Kagome Lattice with Long-range Interactions
• Two-Dimensional Higher-Order Topological Metals
• Bulk-boundary-transport correspondence of the second-order topological insulators
• Unveiling Higher-Order Topology via Polarized Topological Charges
• Higher-order topology in twisted multilayer systems: a review
• Deployable Nanoelectromechanical Bound States in the Continuum Enabled by GHz Lamb Wave Phononic Crystals on LiNbO3 Thin Films
• Dimensional hierarchy of topological bound states in the continuum
• Topological semimetal with coexisting nodal points and nodal lines
• Fragile dislocation modes in obstructed atomic topological phases
• Breakdown of the symmetry constraint in a Floquet topological insulator
• Anti-higher-order Weyl semimetal
• Uncovering Bound States in the Continuum in InSb nanowire networks