title: Topological Creation of Acoustic Pseudospin Multipoles in a Flow-Free Symmetry-Broken Metamaterial Lattice.
abstract: The discovery of topological acoustics has revolutionized fundamental concepts of sound propagation, giving rise to strikingly unconventional acoustic edge modes immune to scattering. Because of the spinless nature of sound, the "spinlike" degree of freedom crucial to topological states in acoustic systems is commonly realized with circulating background flow or preset coupled resonator ring waveguides, which drastically increases the engineering complexity. Here we realize the acoustic pseudospin multipolar states in a simple flow-free symmetry-broken metamaterial lattice, where the clockwise (anticlockwise) sound propagation within each metamolecule emulates pseudospin down (pseudospin up). We demonstrate that tuning the strength of intermolecular coupling by simply contracting or expanding the metamolecule can induce the band inversion effect between the pseudospin dipole and quadrupole, which leads to a topological phase transition. Topologically protected edge states and reconfigurable topological one-way transmission for sound are further demonstrated. These results provide diverse routes to construct novel acoustic topological insulators with versatile applications.
authors.affiliation: Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Zhiwang
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wei
authors.affiliation: Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|State Key Laboratory of Acoustics, Chinese Academy of Science, Beijing 100190, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Cheng
authors.affiliation: Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: School of Physics and Technology, Nanjing Normal University, Nanjing 210046, China.
authors.forename: Dajian
authors.initials: D
authors.lastname: Wu
authors.affiliation: Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|State Key Laboratory of Acoustics, Chinese Academy of Science, Beijing 100190, China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Liu