Alice Kunin (Stony Brook University) -Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors

February 28, 2023

3:45PM - 4:45PM

1080 Physics Research Building

Add to Calendar 2023-02-28 16:45:00 2023-02-28 17:45:00 Alice Kunin (Stony Brook University) -Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors Dr. Alice Kunin Stony Brook University Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors Location: 1080 Physics Research Building, Smith Seminar Room Faculty Host: Louis DiMauro Abstract: Monolayer transition metal dichalcogenides (TMDs) are direct band gap semiconductors that have generated immense interest in recent years for their potential in a variety of optoelectronic applications due to their strong light absorption and emission and unique spin-valley optical selection rules. The remarkable properties of these materials are governed by strongly bound excitons that exhibit a variety of complex optically bright as well as optically dark exciton states that have been, until now, difficult to characterize with current experimental capabilities. In this talk, I will first show how time- and angle-resolved photoemission spectroscopy can be implemented as a powerful tool to directly image the ultrafast dynamics of both bright and dark excitons in micron-sized TMD monolayers in momentum space across the full Brillouin zone. I will then present our recent experimental results imaging the formation and relaxation dynamics of different types of exciton states in monolayer WS2. With circularly polarized photoexcitation, we observe the initial preparation of valley-polarized excitons and reveal the surprising conservation of both exciton binding energy as well as momentum in the depolarization process. I will show in detail how these findings compare with different proposed theoretical models for exciton valley depolarization in TMDs. Bio: Alice Kunin is a postdoctoral associate at Stony Brook University in the group of Thomas Allison where she has worked to pioneer a new approach to time- and angle-resolved photoemission spectroscopy, ‘time-resolved momentum microscopy’, by combining frequency comb-based cavity-enhanced high harmonic generation with new surface imaging techniques. She received her PhD in December 2019 from the University of California, Berkeley as a Department of Defense National Defense Science and Engineering Graduate Fellow in the group of Daniel Neumark where she revealed the ultrafast dynamics of transient negative ions of DNA and RNA nucleobase clusters as model systems for low-energy electron damage to DNA. 1080 Physics Research Building OSU ASC Drupal 8 ascwebservices@osu.edu America/New_York public

Add to Calendar 2023-02-28 15:45:00 2023-02-28 16:45:00 Alice Kunin (Stony Brook University) -Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors Dr. Alice Kunin Stony Brook University Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors Location: 1080 Physics Research Building, Smith Seminar Room Faculty Host: Louis DiMauro Abstract: Monolayer transition metal dichalcogenides (TMDs) are direct band gap semiconductors that have generated immense interest in recent years for their potential in a variety of optoelectronic applications due to their strong light absorption and emission and unique spin-valley optical selection rules. The remarkable properties of these materials are governed by strongly bound excitons that exhibit a variety of complex optically bright as well as optically dark exciton states that have been, until now, difficult to characterize with current experimental capabilities. In this talk, I will first show how time- and angle-resolved photoemission spectroscopy can be implemented as a powerful tool to directly image the ultrafast dynamics of both bright and dark excitons in micron-sized TMD monolayers in momentum space across the full Brillouin zone. I will then present our recent experimental results imaging the formation and relaxation dynamics of different types of exciton states in monolayer WS2. With circularly polarized photoexcitation, we observe the initial preparation of valley-polarized excitons and reveal the surprising conservation of both exciton binding energy as well as momentum in the depolarization process. I will show in detail how these findings compare with different proposed theoretical models for exciton valley depolarization in TMDs. Bio: Alice Kunin is a postdoctoral associate at Stony Brook University in the group of Thomas Allison where she has worked to pioneer a new approach to time- and angle-resolved photoemission spectroscopy, ‘time-resolved momentum microscopy’, by combining frequency comb-based cavity-enhanced high harmonic generation with new surface imaging techniques. She received her PhD in December 2019 from the University of California, Berkeley as a Department of Defense National Defense Science and Engineering Graduate Fellow in the group of Daniel Neumark where she revealed the ultrafast dynamics of transient negative ions of DNA and RNA nucleobase clusters as model systems for low-energy electron damage to DNA. 1080 Physics Research Building Department of Physics physics@osu.edu America/New_York public

Dr. Alice Kunin

Stony Brook University

Direct Time- and Momentum-Resolved Imaging of the Ultrafast Dynamics of Excitons in Atomically Thin Semiconductors

Location: 1080 Physics Research Building, Smith Seminar Room

Faculty Host: Louis DiMauro

Abstract:
Monolayer transition metal dichalcogenides (TMDs) are direct band gap semiconductors that have generated immense interest in recent years for their potential in a variety of optoelectronic applications due to their strong light absorption and emission and unique spin-valley optical selection rules. The remarkable properties of these materials are governed by strongly bound excitons that exhibit a variety of complex optically bright as well as optically dark exciton states that have been, until now, difficult to characterize with current experimental capabilities. In this talk, I will first show how time- and angle-resolved photoemission spectroscopy can be implemented as a powerful tool to directly image the ultrafast dynamics of both bright and dark excitons in micron-sized TMD monolayers in momentum space across the full Brillouin zone. I will then present our recent experimental results imaging the formation and relaxation dynamics of different types of exciton states in monolayer WS2. With circularly polarized photoexcitation, we observe the initial preparation of valley-polarized excitons and reveal the surprising conservation of both exciton binding energy as well as momentum in the depolarization process. I will show in detail how these findings compare with different proposed theoretical models for exciton valley depolarization in TMDs.

Bio:

Alice Kunin is a postdoctoral associate at Stony Brook University in the group of Thomas Allison where she has worked to pioneer a new approach to time- and angle-resolved photoemission spectroscopy, ‘time-resolved momentum microscopy’, by combining frequency comb-based cavity-enhanced high harmonic generation with new surface imaging techniques. She received her PhD in December 2019 from the University of California, Berkeley as a Department of Defense National Defense Science and Engineering Graduate Fellow in the group of Daniel Neumark where she revealed the ultrafast dynamics of transient negative ions of DNA and RNA nucleobase clusters as model systems for low-energy electron damage to DNA.