Topologically Protected Exceptional Point with Local Non-Hermitian Modulation in an Acoustic Crystal

Gu, Zhongming; Gao, He; Liu, Tuo; Liang, Shanjun; An, Shuowei; Li, Yong; Zhu, Jie

doi:10.1103/physrevapplied.15.014025

Cited by 20 publications

(7 citation statements)

References 44 publications

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“…Given the successful demonstrations of enhanced sensing in optics and radiofrequencies [78,79], problems remain in these systems such as limited sensitivity due to fabrication imperfection and high intrinsic noise near EP. Potential solutions could be topologically protected EP and exceptional surface that are more robust to undesired perturbations and fabrication errors [114,115]. Besides, non-Hermitian metasurfaces with the abilities of generating superchiral fields [68] can be applied to sensitive chiral molecule sensing in contrast to weak chirality detection by conventional method of circular dichroism spectroscopy.…”

Section: Discussionmentioning

confidence: 99%

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

Li¹,

Cao²,

Li³

et al. 2021

PIER

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Exceptional points are spectral singularities in non-Hermitian systems at which two or more eigenvalues and their corresponding eigenvectors simultaneously coalesce. Originating from quantum theory, exceptional points have attracted significant attention in optics and photonics because their emergence in systems with nonconservative gain and loss elements can give rise to many counterintuitive phenomena. Metasurfaces -two-dimensional artificial electromagnetic materials structured at the subwavelength scale -can provide a versatile platform for exploring such non-Hermitian phenomena through the addition of dissipation and amplification within their unit cells. These concepts enable a wide range of exotic phenomena, including unidirectional propagation, adiabatic mode conversion, and ultrasensitive measurements, which can be harnessed for technological applications. In this article, we review the recent advances in exceptional-point and non-Hermitian metasurfaces. We introduce the basic theory of exceptional point and non-Hermiticity in metasurfaces, highlight important achievements and applications, and discuss the future opportunities of non-Hermitian metasurfaces from basic science to emerging technologies.

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Section: Discussionmentioning

confidence: 99%

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

Li¹,

Cao²,

Li³

et al. 2021

PIER

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“…The results obtained from the finite-element method (FEM) are expressed as hollow blue circles. For comparison and as a qualitative physical explanation, the system can be seen as a two-level system described by the coupled-mode theory (CMT) [43,44],…”

Section: -3mentioning

confidence: 99%

“…To achieve the PT symmetry with balanced gain and loss, we can set ω 1 = ω 2 ≡ ω 0 , κ 12 = κ 21 ≡ κ, and δ 1 = −δ 2 = δ. It is worth noting that δ has a different dimension from the γ we use in the metabeam, and the relation between γ and δ can be determined by fitting the position of the EP in the parameter space [44]. We can translate the coupled mode Eqs.…”

Section: -3mentioning

confidence: 99%

Exceptional Points and Skin Modes in Non-Hermitian Metabeams

Cai

Jin

et al. 2022

Phys. Rev. Applied

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We present a non-Hermitian metabeam exhibiting an exceptional point (EP) induced by enforcing parity-time (PT) symmetry through applied external forces. The EP is formed by the hybridization of two flexural wave modes and its output displacement is enhanced by attaching two pillars on top of the beam. The introduction of a tiny mass perturbation that breaks the PT symmetry leads to a splitting of the eigenfrequencies at the EP with a square-root dependence on the perturbation mass. This effect manifests itself in a splitting of resonant peaks in the frequency response. The enhanced sensitivity of the EP paves the way to the detection of small perturbations such as tiny masses and cracks. Another property of the metabeam is the existence of skin modes whose energies are localized at one end of the beam and can be generated by implementing nonreciprocal feedback interactions between the pillars. We demonstrate that the skin modes are broadband and independent of the excitation positions. From a practical perspective, we show the great potential of skin modes in broadband energy harvesting. Our study proposes approaches to manipulate the non-Hermitian elastic wave phenomena, paving the way for the development of highly sensitive sensors, vibration control, and energy harvesting.

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“…In recent years, non-Hermitian physics has attracted great attention owing to its rich physical significances and various practical applications [1][2][3][4]. Exceptional point (EP) is a unique feature for non-Hermitian systems, which has become a hot topic in photonics [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], mechanics [20][21][22][23][24][25][26], and acoustics [27][28][29][30][31][32][33][34][35][36][37][38][39] owing to its great potential in energy transport. In acoustics, based on parity-time symmetric systems [27][28][29][30][31][32], researchers have realized EP by introducing balanced gain and loss which can be obtained by a pair of electro-acoustic resonators loaded with specifically tailored circuits [30] and by a composite structure composed of...…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, by inserting sound-absorbing sponges in surface holes of coupled cavities, EP can also be obtained in non-Hermitian structures with asymmetric losses [33,34]. Based on exotic characteristics of EPs [29,31,[35][36][37], several advanced acoustic devices have been proposed, such as sound absorber [27], focusing lens [28,32], invisible acoustic sensor [30], and acoustic mirror [38].…”

Section: Introductionmentioning

confidence: 99%

Exceptional Ring by Non-Hermitian Sonic Crystals

Wang¹,

Ge²,

Yuan³

et al. 2023

PIER

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Exceptional point (EP) and exceptional ring (ER) are unique features for non-Hermitian systems, which have recently attracted great attentions in acoustics due to their rich physical significances and various potential applications. Despite the rapid development about the study of the EP and ER in one-dimensional acoustic systems, the realization of them in two-dimensional (2D) non-Hermitian structures is still facing a great challenge. To overcome this, we numerically and theoretically realize an ER in 2D reciprocal space based on a square-lattice non-Hermitian sonic crystal (SC). By introducing radiation loss caused by circular holes of each resonator in a Hermitian SC, we realize the conversion between a Dirac cone and the ER. Based on the theoretical analysis with the effective Hamiltonian, we obtain that the formation of the ER is closely related to different radiation losses of dipole and quadrupole modes in the resonators. Additionally, in the non-Hermitian SC, two eigenfunctions can be merged into a single self-orthogonal one on the ER, which does not exist in the Hermitian SC. Finally, by verifying the existence of the EP with topological characteristics in every direction of 2D reciprocal space, we further demonstrate the ER in the proposed non-Hermitian SC. Our work may provide theoretical schemes and concrete methods for designing various types of non-Hermitian acoustic devices.

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Topologically Protected Exceptional Point with Local Non-Hermitian Modulation in an Acoustic Crystal

Cited by 20 publications

References 44 publications

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

Exceptional Points and Skin Modes in Non-Hermitian Metabeams

Exceptional Ring by Non-Hermitian Sonic Crystals

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