Topological phononic metamaterials

Abstract

The concept of topological energy bands and their manifestations have been demonstrated in condensed matter systems as a fantastic paradigm toward unprecedented physical phenomena and properties that are robust against disorders. Recent years, this paradigm was extended to phononic metamaterials (including mechanical and acoustic metamaterials), giving rise to the discovery of remarkable phenomena that were not observed elsewhere thanks to the extraordinary controllability and tunability of phononic metamaterials as well as versatile measuring techniques. These phenomena include, but not limited to, topological negative refraction, topological `sasers' (i.e., the phononic analog of lasers), higher-order topological insulating states, non-Abelian topological phases, higher-order Weyl semimetal phases, Majorana-like modes in Dirac vortex structures and fragile topological phases with spectral flows. Here we review the developments in the field of topological phononic metamaterials from both theoretical and experimental perspectives with emphasis on the underlying physics principles. To give a broad view of topological phononics, we also discuss the synergy with non-Hermitian effects and cover topics including synthetic dimensions, artificial gauge fields, Floquet topological acoustics, bulk topological transport, topological pumping, and topological active matters as well as potential applications, materials fabrications and measurements of topological phononic metamaterials. Finally, we discuss the challenges, opportunities and future developments in this intriguing field and its potential impact on physics and materials science.

Dual-functional pentamode metamaterial with water-like and topological transmission properties

“…The symmetry of the hexagonal primitive cell is broken with the rotation angle, the Dirac point is opened and the edge states induced by the quantum valley Hall effect are robust to bending defects. Subsequently, topological metamaterials [31][32][33] with different structural types have also been studied.…”

Low-frequency broadband valley transport for acoustic topology based on extended resonance

“…Some researchers have broken this limitation by constructing multiple bands [21][22][23]. Other researchers have refined the system with different acoustic topologies for different frequency band ranges [26][27][28][29][30][31][32]. Another effective solution is to achieve the controllability of bands [25].…”

Valley edge states with opposite chirality in temperature dependent acoustic media

“…The field of acoustic topological QVHE is experiencing rapid advancement due to its adaptability and variety, offering a new avenue for manipulating the propagation of acoustic waves [23][24][25][26][27]. Numerous captivating subjects related to valley properties have been explored, such as topological oneway edge states [2,3,28], acoustic topological insulators [29,30], acoustic topological rainbow trapping [31,32] and topological valley transport [14,33,34].…”