Hybrid-order topological insulators in a phononic crystal

Abstract

Topological phases, including the conventional first-order and higher-order topological insulators and semimetals, have emerged as a thriving topic in the fields of condensed-matter physics and material science. Usually, a topological insulator is characterized by a fixed order topological invariant and exhibits associated bulk-boundary correspondence. Here, we realize a new type of topological insulator in a bilayer phononic crystal, which hosts simultaneously the first-order and second-order topologies, referred here as the hybrid-order topological insulator. The one-dimensional gapless helical edge states, and zero-dimensional corner states coexist in the same system. The new hybrid-order topological phase may produce novel applications in topological acoustic devices.

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References in corpus (11)

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Cited by in corpus (3)

• Anti-chiral edge states and hinge states based on the Haldane model
• Nonlinear control of photonic higher-order topological bound states in the continuum
• Realization of second-order photonic square-root topological insulators