Topological phases of matter are classified based on their Hermitian Hamiltonians, whose real-valued dispersions together with orthogonal eigenstates form nontrivial topology. In the recently discovered higher-order topological insulators (TIs), the bulk topology can even exhibit hierarchical features, leading to topological corner states, as demonstrated in many photonic and acoustic artificial materials. Naturally, the intrinsic loss in these artificial materials has been omitted in the topology definition, due to its non-Hermitian nature; in practice, the presence of loss is generally considered harmful to the topological corner states. Here, we report the experimental realization of a higher-order TI in an acoustic crystal, whose nontrivial topology is induced by deliberately introduced losses. With local acoustic measurements, we identify a topological bulk bandgap that is populated with gapped edge states and in-gap corner states, as the hallmark signatures of hierarchical higher-order topology. Our work establishes the non-Hermitian route to higher-order topology, and paves the way to exploring various exotic non-Hermiticity-induced topological phases.
Fudan University（复旦大学）；State Key Laboratory of Surface Physics and Institute for Nanoelectronic Devices and Quantum Computing, Fudan University（复旦大学表面物理国家重点实验室和纳米电子器件与量子计算研究所）；Department of Physics, Fudan University（复旦大学物理系）；Zhangjiang Fudan International Innovation Center, Fudan University（复旦大学张江国际创新中心）
Dynamical control of non-hermitian coupling between sub-threshold nanolasers enables Q-switched pulse generation
Technical University of Denmark（丹麦技术大学）；NanoPhoton - Center for Nanophotonics（纳米光子学中心）；Institut de Physique de Nice, CNRS, Université Côte d’Azur（尼斯物理研究所，法国国家科学研究中心，蔚蓝海岸大学）
Symmetry as a route to generalized bosonic Kitaev chains
Pritzker School of Molecular Engineering, The University of Chicago（芝加哥大学普里茨克分子工程学院）；Université Côte d’Azur, CNRS, Centrale Med, Institut de Physique de Nice（蔚蓝海岸大学、法国国家科学研究中心、中央理工-地中海学院、尼斯物理研究所）
Algebraic States in Continuum in $ d\gt 1$ Dimensional Non-Hermitian Systems
Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所，北京凝聚态物理国家研究中心）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Physics, University of Michigan Ann Arbor（密歇根大学安娜堡分校物理系）；Kavli Institute for Theoretical Sciences, Chinese Academy of Sciences（中国科学院理论科学卡弗里研究所）
Arbitrary Control of Non-Hermitian Skin Modes via Disorder and An Electric Field
School of Physics and Optoelectronics, South China University of Technology（华南理工大学物理与光电工程学院）；Research Institute of Future Technology, South China Normal University（华南师范大学未来技术研究院）；State Key Laboratory of Luminescent Materials and Devices and Institute of Optical Communication Materials, South China University of Technology（华南理工大学发光材料与器件国家重点实验室及光通信材料研究所）；Center for Quantum Computing, RIKEN（理研量子计算中心）；Department of Physics, University of Michigan（密歇根大学物理系）
Higher-order exceptional ring semimetal with real hinge states in phononic crystals
Key Laboratory of Artificial Micro- and Nanostructures of Ministry of Education and School of Physics and Technology, Wuhan University（教育部人工微结构和科学与技术学院，武汉大学）；Institute for Advanced Studies, Wuhan University（武汉大学高等研究院）
Observation of Erratic Non-Hermitian Skin Effect in Phononic Crystals
Institute of Acoustics, School of Physics Science and Engineering, Tongji University（同济大学物理科学与工程学院声学研究所）；School of Advanced Manufacturing Engineering, Nanjing University（南京大学先进制造工程学院）
Higher-winding phases in one-dimensional non-Hermitian topological superconductors
Institute of Physics, Academia Sinica（中央研究院物理研究所）；Department of Physics, National Taiwan University（国立台湾大学物理系）；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；Physics Division, National Center for Theoretical Sciences（国家理论科学中心物理组）
Boundary Floquet Control of Bulk non-Hermitian Systems
Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；National University of Singapore（新加坡国立大学）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（粤港澳大湾区量子科学中心）；Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）
Noise-Induced Resurrection of Dynamical Skin Effects in Quasiperiodic Non-Hermitian Systems
School of Physics, Peking University（北京大学物理学院）；Collaborative Innovation Center of Quantum Matter（量子物质协同创新中心）；Center for High Energy Physics, Peking University（北京大学高能物理中心）
Observation of Erratic Non-Hermitian Skin Localization and Transport
Nanjing University（南京大学）；The Pennsylvania State University（宾夕法尼亚州立大学）；Politecnico di Milano（米兰理工大学）；IFISC (UIB-CSIC), Instituto de Fisica Interdisciplinary Sistemas Complejos（复杂系统跨物理研究所（巴伊拉大学-西班牙国家科研委员会））
