Anomalous Collision of Exceptional Points on Nonorientable Manifolds
Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology, Wuhan University（教育部人工微纳结构重点实验室与物理科学与技术学院，武汉大学）
Weijia Wang, Qicheng Zhang, Kun Zhang, Shuaishuai Tong, Chunyin Qiu
Band degeneracies, ranging from Hermitian Dirac points to non-Hermitian exceptional points (EPs), play a central role in topological phase transitions. Beyond the topology of individual degeneracies, their mutual interactions yield richer phenomena. A representative example is the anomalous non-annihilating collision of pairwise-created degeneracies, previously believed to occur only in non-Abelian multiband systems. Here, we theoretically reveal and experimentally demonstrate that such an anomalous collision can emerge even in a simple two-band system without non-Abelian nature. In a two-dimensional non-Hermitian lattice whose Brillouin zone forms a nonorientable Klein bottle, two EPs with opposite topological charges, pairwise created from a hybrid point, merge into a new vortex point upon re-encounter, instead of annihilating. Remarkably, the hybrid point is a defective degeneracy featuring no eigenenergy braiding, whereas the vortex point is a non-defective degeneracy yet exhibits nontrivial eigenenergy braiding. This process manifests a non-Hermitian phase transition from a gapped phase to a gapless phase, a scenario that we directly observe in a hybrid-dimensional acoustic lattice via momentum-resolved band braid and Berry phase measurements. Our findings identify nonorientability as a new arena for engineering band degeneracies and topological phases, and pave the way for experimentally exploring the interplay between exceptional and nonorientable topology.
Non-Hermitian Exceptional Topology on a Klein Bottle Photonic Circuit
KTH Royal Institute of Technology（皇家理工学院）；Stockholm University（斯德哥尔摩大学）；Rochester Institute of Technology（罗切斯特理工学院）；Huazhong University of Science and Technology（华中科技大学）
Anomalous transport in quasiperiodic lattices: emergent exceptional points at band edges and log-periodic oscillations
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）
Signatures of unconventional superconductivity near reentrant and fractional quantum anomalous Hall insulators
Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Hong Kong University of Science and Technology（香港科技大学）；University of Tennessee（田纳西大学）；Fudan University（复旦大学）；Southern University of Science and Technology (SUSTech)（南方科技大学）；National Institute for Materials Science（国立材料研究所）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；Hefei National Laboratory（合肥国家实验室）；Min H. Kao Department of Electrical Engineering and Computer Science, University of Tennessee（田纳西大学明H. Kao电气与计算机工程系）
Non-Hermitian Topology from Edge Transport in Hermitian Quantum Anomalous Hall Systems
International Center for Quantum Materials, School of Physics, Peking University（北京大学物理学院量子材料国际中心）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；School of Physical Science and Technology, Soochow University（苏州大学物理科学与技术学院）；Institute for Advanced Study, Soochow University（苏州大学前沿科学高等研究院）；Institute for Nanoelectronic Devices and Quantum Computing, Fudan University（复旦大学纳米电子器件与量子计算研究所）；Hefei National Laboratory（合肥国家实验室）
