Observation of topological valley transport of sound in sonic crystals

Lu, Jiuyang; Qiu, Chunyin; Ye, Liping; Fan, Xiying; Ke, Manzhu; Zhang, Fan; Liu, Zhengyou

doi:10.1038/nphys3999

Cited by 794 publications

(632 citation statements)

References 35 publications

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“…First, our design is based on a four-band model that allows polarization multiplexing. Thus two pairs of kink states with transverse-electric (TE) and transverse-magnetic (TM) polarizations can be selectively excited, whereas previous studies based on the two-band model, including the recently reported topological valley transport of sound 21,22 , can host only one pair of kink states in a monolayer structure. Second, the kink states can out-couple, or refract, with nearperfect efficiency into ambient space, with promising applications for directional antennas 23 , lasers and displays based on topological modes.…”

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confidence: 97%

Topologically protected refraction of robust kink states in valley photonic crystals

et al. 2017

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Recently discovered1,2 valley photonic crystals (VPCs) mimic many of the unusual properties of two-dimensional (2D) gapped valleytronic materials [3][4][5][6][7][8][9] . Of the utmost interest to optical communications is their ability to support topologically protected chiral edge (kink) states [3][4][5][6][7][8][9] at the internal domain wall between two VPCs with opposite valley-Chern indices. Here we experimentally demonstrate valley-polarized kink states with polarization multiplexing in VPCs, designed from a spin-compatible four-band model. When the valley pseudospin is conserved, we show that the kink states exhibit nearly perfect out-coupling e ciency into directional beams, through the intersection between the internal domain wall and the external edge separating the VPCs from ambient space. The out-coupling behaviour remains topologically protected even when we break the spin-like polarization degree of freedom (DOF), by introducing an e ective spin-orbit coupling in one of the VPC domains. This also constitutes the first realization of spin-valley locking for topological valley transport.

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confidence: 97%

Topologically protected refraction of robust kink states in valley photonic crystals

et al. 2017

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“…However, due to the large separation in k-space of the two valleys, valley-dependent topological invariants can be defined and used to classify the topological states of the different lattices. This approach, usually referred to as quantum valley Hall effect (QVHE), was recently investigated for application to fluidic acoustic waveguides 9,12 , as well as elastic plates with local resonators 28,29 .…”

Section: Introductionmentioning

confidence: 99%

“…Following the groundbreaking research in solid state physics, which showed the existence of topological states of matter 1,2 , researchers have been able to formulate the acoustic analogue of selected mechanisms [3][4][5][6][7][8][9][10][11][12] . During the last decade, several studies have investigated topological materials based on broken space-inversion symmetry (SIS).…”

Section: Introductionmentioning

confidence: 99%

Tunable Acoustic Valley–Hall Edge States in Reconfigurable Phononic Elastic Waveguides

2018

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This study investigates the occurrence of acoustic topological edge states in a 2D phononic elastic waveguide due to a phenomenon that is the acoustic analogue of the quantum valley Hall effect. We show that a topological transition takes place between two lattices having broken space inversion symmetry due to the application of a tunable strain field. This condition leads to the formation of gapless edge states at the domain walls, as further illustrated by the analysis of the bulk-edge correspondence and of the associated topological invariants. Although time reversal symmetry is still intact in these systems, the edge states are topologically protected when inter-valley mixing is either weak or negligible. Interestingly, topological edge states can also be triggered at the boundary of a single domain if boundary conditions are properly selected. We also show that the static modulation of the strain field allows tuning the response of the material between the different supported edge states.

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“…Similarly, coupled ring resonator waveguides were proposed analogous to a Floquet insulator [23][24][25]. Beyond that, valley-projected acoustic topological insulators were proposed to obtain backscattering-immune valley transport [30,32]. However, the inherent losses and noise that intrinsically accompany acoustic propagation in moving media, together with considerable fabrication complexities of ring waveguides may become detrimental in future topological applications.…”

mentioning

confidence: 99%

“…Topological states have also been extended to condensed-matter physics based on the quantum Hall effect (QHE) [1,2], the quantum spin Hall effect (QSHE) [3,4], and topological insulators (TIs) [5,6]. Over the past ten years, investigation into new topologically protected edge states has started to grow in other subfields of physics, such as photonics [7][8][9][10][11][12][13][14][15][16], phononics [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], and mechanics [33][34][35][36]. The intrinsic difference between electrons and acoustic waves represents a great challenge in creating the spinlike degree of freedom for sound only possessing longitudinal polarization.…”

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confidence: 99%

Experimental verification of acoustic pseudospin multipoles in a symmetry-broken snowflakelike topological insulator

et al. 2017

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Topologically protected wave engineering in artificially structured media resides at the frontier of ongoing metamaterials research, which is inspired by quantum mechanics. Acoustic analogs of electronic topological insulators have recently led to a wealth of new opportunities in manipulating sound propagation by means of robust edge mode excitations through analogies drawn to exotic quantum states. A variety of artificial acoustic systems hosting topological edge states have been proposed analogous to the quantum Hall effect, topological insulators, and Floquet topological insulators in electronic systems. However, those systems were characterized by a fixed geometry and a very narrow frequency response, which severely hinders the exploration and design of useful applications. Here we establish acoustic multipolar pseudospin states as an engineering degree of freedom in time-reversal invariant flow-free phononic crystals and develop reconfigurable topological insulators through rotation of their meta-atoms and reshaping of the metamolecules. Specifically, we show how rotation forms man-made snowflakelike molecules, whose topological phase mimics pseudospin-down (pseudospin-up) dipolar and quadrupolar states, which are responsible for a plethora of robust edge confined properties and topological controlled refraction disobeying Snell's law. DOI: 10.1103/PhysRevB.96.241306 Topology is a mathematical concept, which describes the properties of space that are preserved under continuous deformations. Topological states have also been extended to condensed-matter physics based on the quantum Hall effect (QHE) [1,2], the quantum spin Hall effect (QSHE) [3,4], and topological insulators (TIs) [5,6]. Over the past ten years, investigation into new topologically protected edge states has started to grow in other subfields of physics, such as photonics [7][8][9][10][11][12][13][14][15][16], phononics [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], and mechanics [33][34][35][36]. The intrinsic difference between electrons and acoustic waves represents a great challenge in creating the spinlike degree of freedom for sound only possessing longitudinal polarization. To resolve this obstacle, analogous unidirectional edge channels have been demonstrated in phononic crystals (PnC), which were constructed with circulating flow fields [18][19][20][21]37] to break the time-reversal symmetry to mimic the QHE. Similarly, coupled ring resonator waveguides were proposed analogous to a Floquet insulator [23][24][25]. Beyond that, valley-projected acoustic topological insulators were proposed to obtain backscattering-immune valley transport [30,32]. However, the inherent losses and noise that intrinsically accompany acoustic propagation in moving media, together with considerable fabrication complexities of ring waveguides may become detrimental in future topological applications. Most recently, phononic "graphene" with double Dirac cones [27][28][29] has been proposed for the design of two-dimensional (2D) acoustic ...

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Observation of topological valley transport of sound in sonic crystals

Cited by 794 publications

References 35 publications

Topologically protected refraction of robust kink states in valley photonic crystals

Topologically protected refraction of robust kink states in valley photonic crystals

Tunable Acoustic Valley–Hall Edge States in Reconfigurable Phononic Elastic Waveguides

Experimental verification of acoustic pseudospin multipoles in a symmetry-broken snowflakelike topological insulator

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