报告题目：Characterization of exceptional-point geometries and the ensuing geometry-dependent skin effects

报 告 人：丁鲲（复旦大学物理学系）

报告时间：2023年3月2日（周四）下午15:00

报告地点：物理科学与技术学院新楼五楼大报告厅（D-503）

报告摘要：

The seemingly simple fact that the eigenvalues of non-Hermitian systems lie in the complex plane adds another layer to topological physics called spectral topology, which does not exist in Hermitian physics. This additional layer and its interplay with the conventional wavefunction topology have recently made non-Hermitian physics a vibrant realm. The eigenvalue singularities and windings are thus pivotal, and we devote ourselves to discussing them here. The exceptional points (EPs) forming by N states, called the order-N EPs (EPNs), can be regarded as eigenvalue singularities. We begin by investigating multiple order-2 exceptional lines (EL2s), a collection of EP2s, from the braiding group viewpoint. Such an advanced approach makes the complex knot structure of eigenvalues and the role of Reidemeister moves theoretically tractable, further leading to experimental demonstrations. By imposing symmetries, the EL2s (EP3s) can evolve to the order-2 exceptional surfaces (EL3s), which begs for an alternative approach to characterize. In the second half, we demonstrate the geometry-dependent skin effects (GDSEs) in reciprocal systems with both theory and experiment. The realization of GDSEs requires a symmetry mismatch between the macroscopic geometry and the microscopic lattice. The spectral areas and point gaps are then expected at the specific crystalline interfaces, leading to the skin effects.

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。

邀请人：肖孟 教授