题目：Non-Hermitian Dirac Cone

时间：2024年5月14日 10:00-11:00

地点：玉泉校区行政楼第二会议室

报告人：Prof. Xue Haoran (薛昊冉)

Biography: Dr. Xue Haoran is currently an Assistant Professor in the Department of Physics at the Chinese University of Hong Kong (CUHK). He obtained his Bachelor's degree at Nanjing University in 2016 and PhD degree at Nanyang Technological University in 2021. Before joining the CUHK, he was a Research Fellow at Nanyang Technological University from 2021 to 2023. His research interests include topological photonics, topological acoustics and non-Hermitian physics. He has published over 50 papers in high-profile journals like Nature, Nature Materials, Nature Physics, Nature Review Materials, Nature Review Physics, Physical Review Letters and Nature Communications, with over 3000 citations.

Abstract: Non-Hermitian systems containing gain or loss commonly host exceptional point degeneracies, not the diabolic points that, in Hermitian systems, play a key role in topological transitions and related phenomena. Non-Hermitian Hamiltonians with parity-time symmetry can have real spectra but generally nonorthogonal eigenstates, impeding the emergence of diabolic points. We introduce a pair of symmetries that induce not only real eigenvalues but also pairwise eigenstate orthogonality. This allows non-Hermitian systems to host Dirac points and other diabolic points. We construct concrete non-Hermitian models exhibiting Dirac cones and demonstrate several Dirac-cone-related phenomena controlled by non-Hermiticity, such as gain-and-loss induced topological phase transition and Landau levels. I will also discuss our recent experiments using optical fiber loops to realize a non-Hermitian massive Dirac cone. Our theory establishes a new connection between non-Hermitian physics and the rich phenomenology of diabolic points.