时间：2024年12月3日（周二）下午15:30-17:00

Time：15:30-17:00, Tuesday, December 3, 2024

主持人: 西湖大学理学院郑昌喜博士

Host: Dr. Changxi Zheng, PI of School of Science, Westlake University

地址：西湖大学云谷校区E10-211教室

Venue: Room E10-211, Yungu Campus

Language：English

语言：英文

闫骏教授

马萨诸塞大学阿默斯特分校

Prof. Jun Yan

Department of Physics, University of Massachusetts Amherst, MA USA

主讲人/Speaker:

Jun Yan is an Associate Professor of Physics at the University of Massachusetts Amherst. Dr. Yan completed his undergraduate study at Nanjing University, and his PhD at Columbia University, where he pioneered on Raman scattering studies of electron-phonon coupling effects in graphene under the supervision of Prof. Aron Pinczuk and Prof. Philip Kim. He held a postdoc position from 2009 at the University of Maryland, College Park in Prof. Michael Fuhrer’s group before joining the UMass Amherst faculty in 2012. In Maryland, Dr. Yan performed charge transport studies of graphene, and developed ultrasensitive photo-detectors based on graphene. At UMass Amherst, Dr. Yan pushed graphene detectors towards sensing TeraHertz radiation, a notoriously challenging spectral range to work on, and developed versatile optical spectroscopy techniques to study quantum materials and 2D atomic layers, with an emphasis on Coulomb interaction and symmetry effects. His current research interests are mainly in the optical and optoelectronic properties of atomically thin crystals and quantum materials.

讲座摘要/Abstract:

The Coulomb interaction between charged particles plays a central role in the behavior of excitonic excitations confined in two-dimensional (2D) hexagonal transition metal dichalcogenide (TMD) semiconductors. While the direct Coulomb interaction effects are fairly intuitive, the exchange part is more subtle. In this talk, I will discuss how Coulomb direct and exchange interactions manifest in excitonic modes residing in TMD atomic layers. In particular, the exchange interaction can act as a pseudo-magnetic field that twists the valley pseudo-spin around, causing significant valley depolarization. We observe ‘random walk’ of pseudo-spin precession that leads to a counter-intuitive scattering induced valley polarization enhancement. In moiré heterojunctions formed by stacking two TMD layers, the pseudo-magnetic field due to Coulomb exchange interaction has a much weaker strength compared to monolayer TMD. Despite that, the exchange interaction is still found to play a dominant role in the valley depolarization process of excitons trapped in the moiré cells.

讲座联系人/Contact:

理学院，钟梦真，邮箱：zhongmengzhen@westlake.edu.cn

School of Science, Mengzhen Zhong, Email: zhongmengzhen@westlake.edu.cn