The topological properties of an object, associated with an integer called the topological
invariant, are global features that cannot change continuously but only through abrupt …

Phononic crystals (PnCs) control the transport of sound and heat similar to the control of
electric currents by semiconductors and metals or light by photonic crystals. Basic and …

Exceptional points and skin effect, as the two distinct hallmark features unique to the non-
Hermitian physics, have each attracted enormous interests. Recent theoretical works reveal …

The concept of topological energy bands and their manifestations have been demonstrated
in condensed matter systems as a fantastic paradigm toward unprecedented physical …

The advancement in electromagnetic metamaterials, which commenced three decades ago,
experienced a rapid transformation into acoustic and elastic systems in the forms of …

Negative refraction of elastic waves has attracted significant research interest due to its
potential prospects in acoustic imaging, communication, and structural health monitoring …

A finite one-dimensional Su-Schrieffer-Heeger (SSH) chain exhibits “zero-energy” boundary-
mode solutions that are protected by chiral symmetry. The breaking of chiral symmetry leads …

Valley interface states, resulting in acoustic valley Hall topological insulators, have recently
become a hot topic in the study of acoustic systems. On the basis of structural diversity and …

Zero-angle refraction of elastic waves in metamaterials has attracted attention for its
extraordinary wave collimation properties. However, earlier implementations relied on the …

Topological insulators have attracted great interest in recent years because of their robust
transports of topological boundary states. Usually, the topological boundary states are …