Observation of Higher-Order Topological States in Acoustic Twisted Moir\'e Superlattice

TL;DR

This study experimentally demonstrates higher-order topological states in acoustic twisted moiré superlattices, revealing new topological phases with edge and corner states in engineered acoustic systems.

Contribution

It is the first to observe higher-order topological states in acoustic moiré superlattices through combined experimental and theoretical analysis.

Findings

Higher-order topological phase with edge and corner states identified

Experimental confirmation via acoustic pump-probe measurements

Band topology characterized by Wannier centers

Abstract

Twisted moir\'e superlattices (TMSs) are fascinating materials with exotic physical properties. Despite tremendous studies on electronic, photonic and phononic TMSs, it has never been witnessed that TMSs can exhibit higher-order band topology. Here, we report on the experimental observation of higher-order topological states in acoustic TMSs. By introducing moir\'e twisting in bilayer honeycomb lattices of coupled acoustic resonators, we find a regime with designed interlayer couplings where a sizable band gap with higher-order topology emerges. This higher-order topological phase host unique topological edge and corner states, which can be understood via the Wannier centers of the acoustic Bloch bands below the band gap. We confirm experimentally the higher-order band topology by characterizing the edge and corner states using acoustic pump-probe measurements. With complementary theory and experiments, our study opens a pathway toward band topology in TMSs.