报告题目：Beyond Closed Wave Systems: Non-Hermiticity and Vacuum Fluctuations

报告人：丁鲲，复旦大学物理学系研究员

时间：2021年7月23日下午17点

地点：友谊校区毅字楼7层会议室

邀请人：樊元成教授

报告摘要：The classical wave system has demonstrated itself as an excellent platform to manipulate classical waves (light, sound, etc.) and realize novel phenomena which are not easy to experimentally investigate in condensed matters. All of these are based on the scattering and eigenvalue forms of the wave equation in which the core quantities are the macroscopic ε and µ (or ρ and Β) obtained from the homogenization or mean field treatment. However, this framework not only ignores the non-Hermiticity coming from the interaction between different (quasi-)particles but also averages out the fast-varying parts and rapid variations of the electrons.

Therefore, the presentation will cover two topics: non-Hermitian physics and Casimir effect. The first part will focus on the exceptional nexus (EX), which is not only a higher-order exceptional point (EP) but also the cusp singularity of multiple exceptional arcs, which are composed of order-2 EPs. The EX possesses a hybrid topological invariant and provides an excellent platform to realize non-Abelian state permutations [1]. The second part will talk about Casimir induced instabilities at metallic surfaces and interfaces. Surface plasmons subject to a surface distortion split asymmetrically in energy resulting in a net lowering of zero-point energy, which gives rise to the instabilities of planar structures. This is because surface plasmon eigenvalues are the square of frequencies, a statement generally true for electromagnetic excitations. This mechanism provides a fundamental length scale limit to planar nanostructures [2].

[1] Science 370, 1077 (2020); Physical Review Letters 127, 034301 (2021).

[2] Physical Review Letters 126, 046802 (2021).

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。

（文图：樊元成/审核：毛东）