4.8 Article

Acoustic non-Hermitian skin effect from twisted winding topology

Journal

NATURE COMMUNICATIONS
Volume 12, Issue 1, Pages -

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41467-021-26619-8

Keywords

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Funding

  1. National Natural Science Foundation of China (NNSFC) [61625502, 61975176, 11961141010, 62175215]
  2. Top-Notch Young Talents Program of China
  3. Fundamental Research Funds for the Central Universities
  4. National Natural Science Foundation of China [11774137, 12174159, 51779107]
  5. State Key Laboratory of Acoustics, Chinese Academy of Science [SKLA202016]
  6. Singapore Ministry of Education [MOE2019-T2-2-085, MOE2016-T3-1-006]

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The experimental realization of the non-Hermitian skin effect in a one-dimensional non-reciprocal acoustic crystal demonstrates unique features such as bipolar localization and Bloch point, revealing previously unnoticed characteristics of NHSE originating from complex non-Hermitian winding topology.
Non-Hermitian skin effect fundamentally challenges the conventional topological description of a system. Here the authors demonstrate a bipolar non-Hermitian skin effect, where bulk eigenstates localize towards two directions, in a one-dimensional non-reciprocal acoustic crystal with twisted topology. 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 observation of physical phenomena originating from complex non-Hermitian winding topology.

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