Acoustic non-Hermitian skin effect from twisted winding topology

• Main Authors: Zhang, Li, Yang, Yihao, Ge, Yong, Guan, Yi-Jun, Chen, Qiaolu, Yan, Qinghui, Chen, Fujia, Xi, Rui, Li, Yuanzhen, Jia, Ding, Yuan, Shou-Qi, Sun, Hong-Xiang, Chen, Hongsheng, Zhang, Baile
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2023
• Subjects: Science::Physics; Non-Hermitian Skin Effect; Twisted Winding Topology
• Online Access: https://hdl.handle.net/10356/164876
• Institution: Nanyang Technological University

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.