Anomalous Topological Edge States in Non-Hermitian Piezophononic Media

Gao, Penglin; Willatzen, Morten; Christensen, Johan

doi:10.1103/physrevlett.125.206402

Cited by 57 publications

(16 citation statements)

References 30 publications

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“…By controlling the non-reciprocal coupling between arbitrary two sites, more complex unconventional topological windings can be achieved in the present acoustic platform. As the NHSE is a manifestation of the breakdown of the conventional bulk-boundary correspondence, it will be interesting to investigate the generalization of bulkboundary correspondence and generalized Brillouin zones in non-Hermitian topological acoustics 13 .…”

Section: Discussionmentioning

confidence: 99%

“…Introducing a boundary will only lead to boundary states, but will not change any bulk property, including the band topology, as considered universally true for all Hermitian, or energyconservative, systems. However, the recently discovered NHSE has shown that non-Hermiticity, originating from loss/gain or non-reciprocity, can cause all the bulk eigenstates to collapse towards the introduced boundary [3][4][5][6][7][8][9][10][11][12][13][14][15] . The complete collapse of bulk bands in NHSE has posed a challenge to the bulk-boundary correspondence 3 -a fundamental principle of topological physics-which states that the band topology derived from the bulk dictates the topological phenomena at the boundary.…”

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confidence: 99%

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Acoustic non-Hermitian skin effect from twisted winding topology

Zhang

Yang

et al. 2021

Preprint

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The recently discovered non-Hermitian skin effect (NHSE) manifests the breakdown of current classification of topological phases in energy-nonconservative systems, and necessitates the introduction of non-Hermitian band topology. So far, all NHSE observations are based on one type of non-Hermitian band topology, in which the complex energy spectrum winds along a closed loop. As recently characterized along a synthetic dimension on a photonic platform, non-Hermitian band topology can exhibit almost arbitrary windings in momentum space, but their actual phenomena in real physical systems remain unclear. Here, we report the experimental realization of NHSE in a one-dimensional (1D) non-reciprocal acoustic crystal. With direct acoustic measurement, we demonstrate that a twisted winding, whose topology consists of two oppositely oriented loops in contact rather than a single loop, will dramatically change the NHSE, following previous predictions of unique features such as the bipolar localization and the Bloch point for a Bloch-wave-like extended state. This work reveals previously unnoticed features of NHSE, and provides the first observation of physical phenomena originating from complex non-Hermitian winding topology.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Acoustic non-Hermitian skin effect from twisted winding topology

Zhang

Yang

et al. 2021

Preprint

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“…Non-Hermitian topological physics [1][2][3][4][5] is attracting a considerable interest since the past few years, with a wealth of novel phenomena which do not have any counterpart in corresponding Hermitian topological systems (see and references therein). The ability to experimentally implement and control non-Hermiticity using synthetic lattices has been demonstrated using different physical platforms ranging from photonic [35,38,39,47,48], acoustic [14,45] and micro mechanical [33,34] systems to topolectrical circuits [36,37].…”

Section: Introductionmentioning

confidence: 99%

Selective and tunable excitation of topological non-Hermitian skin modes

Longhi

2021

Preprint

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Non-Hermitian lattices under semi-infinite boundary conditions sustain an extensive number of exponentiallylocalized states, dubbed non-Hermitian skin modes. Such states can be predicted from the nontrivial topology of the energy spectrum under periodic boundary conditions via a bulk-edge correspondence. However, the selective excitation of the system in one among the infinitely-many topological skin edge states is challenging both from practical and conceptual viewpoints. In fact, in any realistic system with a finite lattice size most of skin edge states collapse and become metastable states. Here we suggest a route toward the selective and tunable excitation of topological skin edge states which avoids the collapse problem by emulating semi-infinite lattice boundaries via tailored on-site potentials at the edges of a finite lattice. We illustrate such a strategy by considering a non-Hermitian topological interface obtained by connecting two Hatano-Nelson chains with opposite imaginary gauge fields, which is amenable for a full analytical treatment.

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“…It works, for example, for the aforementioned Chern insulator and Z 2 topological insulator with manifestation as gapless chiral and helical edge states, respectively. However, this relationship turns out to be faced with the demanding for modification at least by two cases: non-Hermitian [26][27][28][29][30] and higher-order topo-logical systems [31][32][33][34][35][36]. In the former case, one-by-one situations need corresponding generalizations, and in the latter case there are simply no gapless boundary states at all on boundaries with unit-lower dimensions.…”

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confidence: 99%

Topological Corner States in Graphene by Bulk and Edge Engineering

Zeng¹,

Chen²,

Ren³

et al. 2022

Preprint

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Two-dimensional higher-order topology is usually studied in (nearly) particle-hole symmetric models, so that an edge gap can be opened within the bulk one. But more often deviates the edge anticrossing even into the bulk, where corner states are difficult to pinpoint. We address this problem in a graphene-based Z2 topological insulator with spin-orbit coupling and in-plane magnetization both originating from substrates through a Slater-Koster multi-orbital model. The gapless helical edge modes cross inside the bulk, where is also located the magnetization-induced edge gap. After demonstrating its second-order nontriviality in bulk topology by a series of evidence, we show that a difference in bulk-edge onsite energy can adiabatically tune the position of the crossing/anticrossing of the edge modes to be inside the bulk gap. This can help unambiguously identify two pairs of topological corner states with nonvanishing energy degeneracy for a rhombic flake. We further find that the obtuse-angle pair is more stable than the acute-angle one. These results not only suggest an accessible way to "find" topological corner states, but also provide a higher-order topological version of "bulk-boundary correspondence".

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Anomalous Topological Edge States in Non-Hermitian Piezophononic Media

Cited by 57 publications

References 30 publications

Acoustic non-Hermitian skin effect from twisted winding topology

Acoustic non-Hermitian skin effect from twisted winding topology

Selective and tunable excitation of topological non-Hermitian skin modes

Topological Corner States in Graphene by Bulk and Edge Engineering

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