# Pseudospin-valley-coupled phononic topological insulator with edge and corner states

## TL;DR

This paper presents a novel pseudospin-valley-coupled phononic topological insulator that features both gapped edge states and topological corner states, with experimental validation of robust wave propagation and localized resonances.

## Contribution

It introduces a new class of phononic topological insulator with controllable edge and corner states, combining pseudospin and valley coupling effects.

## Key findings

- Demonstration of gapped edge states and topological corner states in phononic systems
- Experimental confirmation of robust edge waveguiding and localized corner modes
- Control over pseudospin-valley coupling enables reconfigurable topological states

## Abstract

Topologically protected gapless edge states are phases of quantum matter which behave as massless Dirac fermions, immunizing against disorders and continuous perturbations. Recently, a new class of topological insulators (TIs) with topological corner states have been theoretically predicted in electric systems, and experimentally realized in two-dimensional (2D) mechanical and electromagnetic systems, electrical circuits, optical and sonic crystals, and elastic phononic plates. Here, we demonstrate a pseudospin-valley-coupled phononic TI, which simultaneously exhibits gapped edge states and topological corner states. Pseudospin-orbit coupling edge states and valley-polarized edge state are respectively induced by the lattice deformation and the symmetry breaking. When both of them coexist, these topological edge states will be greatly gapped and the topological corner state emerges. Under direct field measurements, the robust edge propagation behaving as an elastic waveguide and the topological corner mode working as a robust localized resonance are experimentally confirmed. The pseudospin-valley coupling in our phononic TIs can be well-controlled which provides a reconfigurable platform for the multiple edge and corner states, and exhibits well applications in the topological elastic energy recovery and the highly sensitive sensing.

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Source: https://tomesphere.com/paper/1908.03476