January 25, 2022
Exploring Excitonic Landscape in 2D Semiconductors with Full Vision in Energy, Momentum and Time
Photoexcitation of 2D semiconductors gives rise to electron-hole (e-h) gas in diverse many-body states, varying from unbound plasma states to bound excitonic quasi-particles. These many-body states have been mainly explored by optical methods, but with difficulties to directly access momentum-resolved dark states or to simultaneously monitor materials quasi-particle band responses. Here, by using time- and angle-resolved photoemission spectroscopy, we excite and directly visualize these many-body e-h states, especially the excitonic ones, in monolayer MoS2 with unprecedent fingerprints in energy, momentum, and time. Three questions are addressed in this talk. 1. How do we identify the photoemission signature of these many-body e-h states and further visualize their ultrafast inter-state transition. 2. How would the formation of these states impact the materials quasi-particle band structure. 3. Is it possible to explore wider categories of excitonic phenomena via photoemission probes. We hope these insights could open new possibilities for resolving the intriguing and demanding crossover regimes between different states in correlated quantum materials.
Yi Lin received his bachelor degree (2014) in Physics at Renmin University of China; the master (2015) and PhD degree (2019) in Applied Physics at Columbia University. He is presently a postdoc researcher in the Materials Science Division at Berkeley National Lab. Since his PhD, he has engaged his career in studying and controlling photoexcited quantum materials by combining the power of multifarious ultrafast lasers and electron spectroscopies. Outside his research, he has been an active tenor soloist in bel canto singing. For more info, please refer to his personal page: https://yilin.lbl.gov/