报告人简介：

丁鲲青年研究员2013年毕业于复旦大学物理学系并获博士学位，导师为周磊教授。2013-2018年，他于香港科技大学高等研究院和物理系先后担任博士后和科研助理教授，导师是陈子亭教授 (Prof. C. T. Chan); 2019-2020年，他在英国帝国理工学院Sir John B.Pendry教授课题组从事博士后研究。2021年1月丁鲲青年研究员加入复旦大学物理学系，近年来主要的研究方向为经典波系统的非厄米物理、等离子体激元和涨落物理。

摘要：

The seemingly simple fact that the eigenvalues of non-Hermitiansystems lie in the complex plane adds another layer to topological physicscalled spectral topology, which does not exist in Hermitian physics. Thisadditional layer and its interplay with the conventional wavefunctiontopology have recently made non-Hermitian physics a vibrant realm. Theeigenvalue singularities and windings are thus pivotal, and we devoteourselves to discussing them here. The exceptional points (EPs) forming byN states, called the order-NEPs (EPNs), can be regarded as eigenvaluesingularities. We begin by investigating multiple order-2 exceptional lines(EL2s), a collection of EP2s, from the braiding group viewpoint. Such anadvanced approach makes the complex knot structure of eigenvalues and therole of Reidemeister moves theoretically tractable, further leading toexperimental demonstrations. By imposing symmetries, the EL2s (EP3s) canevolve to the order-2 exceptional surfaces (EL3s), which begs for analternative approach to characterize. In the second half, we demonstrate thegeometry-dependent skin effects (GDSEs) in reciprocal systems with boththeory and experiment. The realization of GDSEs requires a symmetrymismatch between the macroscopic geometry and the microscopic lattice.The spectral areas and point gaps are then expected at the specific crystallineinterfaces, leading to the skin effects.