Three-dimensional valley-contrasting sound

Abstract

Spin and valley are two fundamental properties of electrons in crystals. The similarity between them is well understood in valley-contrasting physics established decades ago in two-dimensional (2D) materials like graphene--with broken inversion symmetry, the two valleys in graphene exhibit opposite orbital magnetic moments, similar to the spin-1/2 behaviors of electrons, and opposite Berry curvature that leads to a half topological charge. However, valley-contrasting physics has never been explored in 3D crystals. Here, we develop a 3D acoustic crystal exhibiting 3D valley-contrasting physics. Unlike spin that is fundamentally binary, valley in 3D can take six different values, each carrying a vortex in a distinct direction. The topological valley transport is generalized from the edge states of 2D materials to the surface states of 3D materials, with interesting features including robust propagation, topological refraction, and valley-cavity localization. Our results open a new route for wave manipulation in 3D space.

arXiv comment8 pages, 5 figures

References in corpus (29)

• Quantum Spin Hall Effect in Graphene
• Berry Phase Effects on Electronic Properties
• Electronic Structure of Pyrochlore Iridates: From Topological Dirac Metal to Mott Insulator
• Topological Insulators in Three Dimensions
• Valley contrasting physics in graphene: magnetic moment and topological transport
• Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineering
• The Valley Hall Effect in MoS2 Transistors
• Chern Numbers in Discretized Brillouin Zone: Efficient Method of Computing (Spin) Hall Conductances
• Valley Dependent Optoelectronics from Inversion Symmetry Breaking
• Observation of topological valley transport of sound in sonic crystals
• Topological nodal line semimetals
• Detecting Topological Currents in Graphene Superlattices
• All-Si Valley-Hall Photonic Topological Insulator
• Topolectrical circuits
• Berry phase, hyperorbits, and the Hofstadter spectrum: semiclassical dynamics in magnetic Bloch bands
• Topologically-protected refraction of robust kink states in valley photonic crystals
• Topological acoustics
• Valley Vortex States in Sonic Crystals
• Observation of a single-beam gradient force acoustical trap for elastic particles: acoustical tweezers
• Realization of an acoustic third-order topological insulator
• Experimental Measurement of the Berry Curvature from Anomalous Transport
• Minimal model for higher-order topological insulators and phosphorene
• Magnetic control of the valley degree of freedom of massive Dirac fermions with application to transition metal dichalcogenides
• Observation of strong backscattering in valley-Hall photonic topological interface modes
• Experimental characterization of fragile topology in an acoustic metamaterial
• Observation of Edge Solitons in Photonic Graphene
• A Topology-Controlled Photonic Cavity Based on the Near-Conservation of the Valley Degree of Freedom
• Strain-induced Landau Levels in arbitrary dimensions with an exact spectrum
• Three-dimensional flat Landau levels in an inhomogeneous acoustic crystal