Realization of Surface-Obstructed Topological Insulators

Abstract

Recently, higher-order topological insulators have been attracting extensive interest. Unlike the conventional topological insulators that demand bulk gap closings at transition points, the higher-order band topology can be changed without bulk closure and exhibits as an obstruction of higher-dimensional boundary states. Here, we report the first experimental realization of three-dimensional surface-obstructed topological insulators with using acoustic crystals. Our acoustic measurements demonstrate unambiguously the emergence of one-dimensional topological hinge states in the middle of the bulk and surface band gaps, as a direct manifestation of the higher-order band topology. Together with comparative measurements for the trivial and phase-transition-point insulators, our experimental data conclusively evidence the unique bulk-boundary physics for the surface-obstructed band topology. That is, the topological phase transition is determined by the closure of surface gap, rather than by closing the bulk gap. Our study might spur on new activities to deepen the understanding of such elusive topological phases.

Phys.Rev.Lett. Accepted

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• Topological Phases in Magnonics
• Higher-order topological phases in crystalline and non-crystalline systems: a review
• Unified characterization for higher-order topological phase transitions
• Higher-Order Topological Insulators via Momentum-Space Nonsymmorphic Symmetries
• Unveiling Higher-Order Topology via Polarized Topological Charges
• Bulk-boundary-transport correspondence of the second-order topological insulators
• Boundary obstructed topological superconductor in buckled honeycomb lattice under perpendicular electric field
• Topological Phases in Non-Hermitian Nonlinear-Eigenvalue Systems
• Proposal for realizing and probing topological crystalline insulators in optical lattices
• Synchronized in-gap edge states and robust copropagation in topological insulators without magnetic flux
• Breakdown of the symmetry constraint in a Floquet topological insulator