Observation of a $p$-orbital higher-order topological insulator phase in puckered lattice acoustic metamaterials

TL;DR

This paper demonstrates the existence of a higher-order topological insulator phase in puckered lattice acoustic metamaterials driven by $p$-orbitals, confirmed through experiments and simulations, revealing unique boundary states.

Contribution

It introduces the first observation of $p$-orbital higher-order topology in puckered acoustic lattices, highlighting the role of geometry and orbital type in topological phases.

Findings

Confirmation of edge and corner states via acoustic measurements.

Identification of $p$-orbital specific higher-order topology.

Analysis of boundary states using Wannier orbitals.

Abstract

The puckered lattice geometry, along with $p$-orbitals is often overlooked in the study of topological physics. Here, we investigate the higher-order topology of the $p_{x,y}$-orbital bands in acoustic metamaterials using a simplified two-dimensional phosphorene lattice which possesses a puckered structure. Notably, unlike the $s$-orbital bands in planar lattices, the unique higher-order topology observed here is specific to $p$-orbitals and the puckered geometry due to the unusual hopping patterns induced by them. {Using acoustic pump-probe measurements in metamaterials}, we confirm the emergence of the edge and corner states arising due to the unconventional higher-order topology. We reveal the uniqueness of the higher-order topological physics here via complimentary tight-binding calculations, finite-element simulations, and acoustic experiments. We analyze the underlying physics of the special properties of the edge and corner states in the puckered lattice acoustic metamaterials from the picture of Wannier orbitals. Our work sheds light on the intriguing physics of $p$-orbital topological physics in puckered lattices and acoustic metamaterials which lead to unconventional topological boundary states. \end{abstract}