Acoustic Tamm states in slender tubes

Khattou, Soufyane; Amrani, Madiha; Mouadili, A.; Boudouti, El Houssaine El; Djafari‐Rouhani, Bahram

doi:10.1016/j.matpr.2021.01.504

Cited by 3 publications

(1 citation statement)

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“…Particularly, great interest has been paid to localized surface modes called Tamm states [15], which were originally discovered for electrons in condensed matter physics. Later, Tamm states have been extended to classical wave systems such as acoustics [16][17][18], photonics [19][20][21] and plasmonics [22].…”

Section: Introductionmentioning

confidence: 99%

Tunable Topological Acoustic Tamm States in Comblike Structures Based on Band Inversion around Flat Bands

et al. 2022

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We investigate the existence of acoustic Tamm states at the interface between two one-dimensional (1D) comblike phononic crystals (PnCs) based on slender tubes and discuss their topological or trivial character. The PnCs consist of stubs grafted periodically along a waveguide and the two crystals differ by their geometrical parameters (period and length of the stubs). We use several approaches to discuss the existence of Tamm states and their topology when connecting two half-crystals. First, we derive a necessary and sufficient condition on the existence of interface states based on the analysis of the bulk band structure and the symmetry of the band edge states. This approach is equivalent to an analysis of the Zak phases of the bulk bands in the two crystals. Indeed, a topological interface state should necessarily exist in any common bandgap of the two PnCs for which the lower (upper) band edges have opposite symmetries. A novelty of our structure consists in the fact that the symmetry inversion results from a band closure (flat band) rather than from a gap closure, in contrast to previous works. Then, such interface states are revealed through different physical quantities, namely: (i) the local density of states (LDOS), which exhibits a high localization around the interface; (ii) sharp peaks in the transmission spectra in the common bandgap when two finite crystals are connected together; (iii) the phases of the reflection coefficients at the boundary of each PnC with a waveguide, which have a direct relationship with the Zak phases. In addition, we show that the interface states can transform to bound states in the continuum (BICs). These BICs are induced by the cavity separating both PnCs and they remain robust to any geometrical disorder induced by the stubs and segments around this cavity. Finally, we show the impossibility of interface states between two connected PnCs with different stub lengths and similar periods. The sensitivity of these states to interface perturbations can find many practical applications in PnC sensors.

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Section: Introductionmentioning

confidence: 99%

Tunable Topological Acoustic Tamm States in Comblike Structures Based on Band Inversion around Flat Bands

et al. 2022

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Observations of Tamm modes in acoustic topological insulators

Liao

Yue

Zhang

et al. 2022

Applied Physics Letters

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The existence of topologically protected boundary states in the Su–Schrieffer–Heeger (SSH) model has been widely explored in various systems in the past decades. On the other hand, a seemingly irrelevant phenomenon of Tamm mode, a defect mode caused by elaborately introducing perturbation into the trivial structures, has also attracted enormous interest. In this Letter, we bridge the gap between acoustic Tamm mode and its correlation rule with typical topological acoustic mode. Starting from the 1D acoustic cavity-based SSH model, the topologically protected edge modes in a complete bandgap are achieved. Through modulating the height of boundary cavity, we find two types of Tamm edge modes both numerically and experimentally and grasp their distinct variation tendency from the topologically protected edge modes. Furthermore, we extend the study to 2D higher-order topological acoustic systems and the lower-dimensional Tamm corner modes are clearly observed. We foresee that the multi-frequency sound confinement introduced by the Tamm localized modes may open a revealing landscape for acoustic functional devices.

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