报告人简介：
Dr. Hengxin Tan received his Ph.D. from Tsinghua University in the winter of 2018. He then began his first postdoctoral research at the Max Planck Institute for Microstructure Physics in Germany. In the summer of 2020, he moved to the Weizmann Institute of Science in Israel for a second postdoctoral position. In January 2025, he joined Shanghai Jiao Tong University. His research focuses on computational condensed matter physics, with particular emphasis on the theoretical exploration of novel quantum materials such as kagome systems and topological materials. He maintains extensive collaborations with experimental researchers and has published over 60 peer-reviewed papers, most of which have appeared in the APS and Nature series.

讲座摘要：
The saddle point, also known as the van Hove singularity, represents a critical point in the electronic structure. It is a fundamental feature of the kagome lattice and is believed to be responsible for many intriguing phenomena. In this talk, I will first introduce the role the saddle point plays in the charge density wave (CDW) formation of the widely studied kagome superconductors AV3Sb5 (A=K, Rb, Cs) and the topological semimetal ScV6Sn6. The power of the saddle point in triggering electronic instabilities lies in its divergent density of states (DOS) in two-dimensional (2D) space. In contrast, an ordinary saddle point in three-dimensional (3D) space does not exhibit a pronounced DOS peak, resulting in less common instabilities in 3D materials. I will demonstrate that the DOS of the 3D saddle point can be significantly enhanced through the higher-order saddle point (HOSP), characterized by a higher-order momentum-dependent energy dispersion. The flattened band structure of the 3D HOSP presents more opportunities for fascinating electronic instabilities and correlation effects in 3D materials. Potential material candidates for 3D HOSP will be discussed, along with the relationship between the 3D saddle point and CDW formation in ScV6Sn6.

邀请人：齐彦鹏