Showing papers by "Manzhu Ke published in 2020"

Acoustic Realization of Quadrupole Topological Insulators.

Abstract: A quadrupole topological insulator, being one higher-order topological insulator with nontrivial quadrupole quantization, has been intensely investigated very recently. However, the tight-binding model proposed for such emergent topological insulators demands both positive and negative hopping coefficients, which imposes an obstacle in practical realizations. Here, we introduce a feasible approach to design the sign of hopping in acoustics, and construct the first acoustic quadrupole topological insulator that stringently emulates the tight-binding model. The inherent hierarchy quadrupole topology has been experimentally confirmed by detecting the acoustic responses at the bulk, edge, and corner of the sample. Potential applications can be anticipated for the topologically robust in-gap states, such as acoustic sensing and energy trapping.

Valley-locked waveguide transport in acoustic heterostructures.

Abstract: Valley pseudospin, labeling the pair of energy extrema in momentum space, has been attracting attention because of its potential as a new degree of freedom in manipulating electrons or classical waves. Recently, topological valley edge transport of sound, by virtue of the gapless valley-locked edge states, has been observed in the domain walls of sonic crystals. Here, by constructing a heterostructure with sonic crystals, a topological waveguide is realized. The waveguide states feature gapless dispersion, momentum-valley locking, immunity against defects, and a high capacity for energy transport. With a designable size, the heterostructures are more flexible for interfacing with the existing acoustic devices than the domain wall structures. Such heterostructures may serve as versatile new devices for acoustic wave manipulation, such as acoustic splitting, reflection-free guiding and converging.

Symmetry-enforced three-dimensional Dirac phononic crystals.

Abstract: Dirac semimetals, the materials featuring fourfold degenerate Dirac points, are critical states of topologically distinct phases. Such gapless topological states have been accomplished by a band-inversion mechanism, in which the Dirac points can be annihilated pairwise by perturbations without changing the symmetry of the system. Here, we report an experimental observation of Dirac points that are enforced completely by the crystal symmetry using a nonsymmorphic three-dimensional phononic crystal. Intriguingly, our Dirac phononic crystal hosts four spiral topological surface states, in which the surface states of opposite helicities intersect gaplessly along certain momentum lines, as confirmed by additional surface measurements. The novel Dirac system may release new opportunities for studying elusive (pseudo) and offer a unique prototype platform for acoustic applications.

Symmetry-enforced three-dimensional Dirac phononic crystals

Abstract: Dirac semimetals, the materials featured with discrete linearly crossing points (called Dirac points) between four bands, are critical states of topologically distinct phases. Such gapless topological states have been accomplished by a band-inversion mechanism, in which the Dirac points can be annihilated pairwise by perturbations without changing the symmetry of the system. Here, we report an experimental observation of Dirac points that are enforced completely by the crystal symmetry, using a nonsymmorphic three-dimensional phononic crystal. Intriguingly, our Dirac phononic crystal hosts four spiral topological surface states, in which the surface states of opposite helicities intersect gaplessly along certain momentum lines, as confirmed by our further surface measurements. The novel Dirac system may release new opportunities for studying the elusive (pseudo)relativistic physics, and also offer a unique prototype platform for acoustic applications.

Observation of quadratic Weyl points and double-helicoid arcs

Abstract: Novel quasiparticles beyond those mimicking the elementary high-energy particles such as Dirac and Weyl fermions have attracted great interest in condensed-matter physics and materials science. Here we report an experimental observation of the long-desired quadratic Weyl points by using a three-dimensional chiral metacrystal of sound waves. Markedly different from the newly observed unconventional quasiparticles, such as the spin-1 Weyl points and the charge-2 Dirac points featuring respectively threefold and fourfold band crossings, the charge-2 Weyl points identified here are simply twofold degenerate, and the dispersions around them are quadratic in two directions and linear in the third one. Besides the essential nonlinear bulk dispersions, we further unveil the exotic double-helicoid surface arcs that emanate from a projected quadratic Weyl point and terminate at two projected conventional Weyl points. This unique global surface connectivity provides conclusive evidence for the double topological charges of such unconventional topological nodes. Novel topological quasiparticles have attracted many interests recently. Here, He et al. observe quadratic Weyl points and identify double-helicoid surface arcs in sound waves traveling in a three-dimensional chiral metacrystal.

Metafluids beyond the Bulk Modulus.

Abstract: It is well known that the acoustic properties of fluid are characterized by mass density and bulk modulus. Metafluids, the fluid metamaterials, generalize the natural fluid, which can accommodate extreme and/or negative values of these two parameters. Here, we further show that the metafluids, composed of periodic thin-walled hollow cylinders immersed in fluid, can provide not only the designable effective mass density and bulk modulus, but also a completely new effective parameter, which appears in the wave velocities as a role similar to the shear modulus of solid. The new effective parameter, describing the response of the fluid to the quadrupolar component of waves, is obtained by generalizing the effective medium theory (EMT) to include the second-order effects, which is vanishing and neglected in the conventional EMT, but giant here in the metafluids with built-in quadrupolar resonances. With the discovery of the metafluids of shearlike moduli, our Letter extends the concept of metafluids and will have a great significance in the field of metamaterials.

Planar lens and manufacturing method for planar lens

Abstract: A planar lens (100) and a manufacturing method for a planar lens (100) relate to the technical field of lenses, the planar lens (100) being a focusing lens and comprising an acoustic soft material tangible structure (110) and a cover layer (120), the acoustic soft material tangible structure (110) comprises a plurality of combination lenses (130) located in the same plane, each combination lens (130) comprises a circular part (131) and a plurality of concentric annular parts (132) which are continuously arranged around the circular part (131), the thicknesses of each two adjacent annular parts (132) in each combination lens (130) are different, and the thickness of each annular part (132) is related to the focal length of the respective combination lens (130); and the cover layer (120) covers the outer surface of the acoustic soft material tangible structure (110) to form the planar lens (100).