Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                

Acoustic Realization of Surface-Obstructed Topological Insulators

Juan Du, Tianzi Li, Xiying Fan, Qicheng Zhang, and Chunyin Qiu
Phys. Rev. Lett. 128, 224301 – Published 1 June 2022
PDFHTMLExport Citation
Abstract
Authors
Article Text
  • Introduction.—
  • General considerations and tight-binding…
  • Acoustic realizations.—
  • Experimental results.—
  • Conclusions.—
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    Recently, higher-order topological insulators have been attracting extensive interest. Unlike the conventional topological insulators that demand bulk gap closings at transition points, the higher-order band topology can be changed without bulk closure and exhibits as an obstruction of higher-dimensional boundary states. Here, we report the first experimental realization of three-dimensional surface-obstructed topological insulators with using acoustic crystals. Our acoustic measurements demonstrate unambiguously the emergence of one-dimensional topological hinge states in the middle of the bulk and surface band gaps, as a direct manifestation of the higher-order band topology. Together with comparative measurements for the trivial and phase-transition-point insulators, our experimental data conclusively evidence the unique bulk-boundary physics for the surface-obstructed band topology. That is, the topological phase transition is determined by the closure of the surface gap, rather than by closing the bulk gap. Our study might spur on new activities to deepen the understanding of such elusive topological phases.

    • Figure
    • Figure
    • Figure
    • Figure
    • Received 29 November 2021
    • Accepted 11 April 2022

    DOI:https://doi.org/10.1103/PhysRevLett.128.224301

    © 2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Acoustic metamaterialsTopological materials
    Condensed Matter, Materials & Applied PhysicsInterdisciplinary PhysicsGeneral Physics

    Authors & Affiliations

    Juan Du*, Tianzi Li*, Xiying Fan, Qicheng Zhang, and Chunyin Qiu†

    • Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China

    • *These authors contributed equally to this work.
    • †To whom correspondence should be addressed. cyqiu@whu.edu.cn

    Article Text (Subscription Required)

    Click to Expand

    Supplemental Material (Subscription Required)

    Click to Expand

    References (Subscription Required)

    Click to Expand
    Issue

    Vol. 128, Iss. 22 — 3 June 2022

    Reuse & Permissions
    Access Options
    Author publication services for translation and copyediting assistance advertisement

    Authorization Required

    Log In
    Other Options
    ×

    Images

    • Figure 1
      Figure 1

      Tight-binding model. (a) Schematic illustration for realizing a SOTI. (b) Extended 2D SSH model and our AB-stacked 3D unit cell. The layers A and B carry opposite in-plane couplings, as indicated by the solid and dashed lines. (c) 3D phase diagram plotted with three typical slices. (d) Energy spectra simulated for finite lattices with fixed in-plane couplings but different interlayer couplings characterized by Δ=λz−γz. The phase transition happens exactly at Δ=0, featuring clearly a gap closure of the yz-surface states (blue) and the emergence of the y-directed hinge states (red).

      Reuse & Permissions
    • Figure 2
      Figure 2

      Full-wave simulations for our acoustic crystals. (a) 3D unit cell made of air cavities (gray) and narrow tubes (color). The sizes of the vertical tubes are tuned to realize topological phase transition, and the in-plane couplings are flipped by the different connectivity between the cavities. (b) Eigenfrequency spectra simulated for three typical acoustic samples of finite sizes. (c) and (d) Averaged intensity distributions of the bulk and boundary states extracted for samples 1 and 3, respectively.

      Reuse & Permissions
    • Figure 3
      Figure 3

      Experimental measurements. (a) Photograph exemplified for the sample 3. The red and blue stars indicate the locations of the sound source and detector, respectively. Inset: a local view of the sample, which displays the z-directed coupling tubes more clearly. (b) Surface domains of the samples divided for calculating average intensity spectra of different states. (c)–(e) Average intensity spectra measured for the bulk, surface, and hinge states (if any) in the three samples. Shaded regions denote the frequency ranges counted for the spatial intensity distributions in Fig. 4. (f)–(h): Numerical comparisons for (c)–(e). All experimental data reproduce well the simulation results.

      Reuse & Permissions
    • Figure 4
      Figure 4

      Field distributions over the sample surfaces. (a)–(c) Intensity patterns measured for different types of states exhibited in the three samples, respectively, integrated over the corresponding frequency ranges shaded in Figs. 3. (d)–(f) Comparative simulation results.

      Reuse & Permissions
    ×

    Sign up to receive regular email alerts from Physical Review Letters

    Log In

    Cancel
    ×

    Search

    Article Lookup

    Paste a citation or DOI
    Enter a citation
    ×