OSC Colloquium: Thomas Allison, "Ultrafast Imaging of Electron and Exciton Dynamics in 2D Materials"

Title: "Ultrafast Imaging of Electron and Exciton Dynamics in 2D Materials" 

Abstract(s): 

Our conceptual pictures and theoretical formulations regarding the dynamics of electrons in crystalline materials, and the related quasiparticles of holes and excitons, are formulated in momentum space. For example, when we think about how a semiconductor absorbs or emits light, we draw the band structure and arrows connecting the valence band and conduction band, along with scattering mechanisms characterized by energy and crystal momentum. 

Optical measurements of these phenomena, however, are always momentum-integrated, and significant interpretation is required to connect optical spectra to the underlying momentum-space dynamics. Recently, breakthroughs in technology for time- and angle-resolved photoemission (tr-ARPES), developed at Stony Brook and a few other labs, make direct momentum-space space snapshots of electron dynamics across the full Brillouin zone no longer just a theoretical construct but a recorded reality. Critically, we can now study dynamics after perturbative excitation to record the intrinsic dynamics of materials relevant for device applications. We can also make measurements on micron-sized samples, which dramatically enlarges the space of materials that can studied with tr-ARPES. 

In this talk, I will discuss both the optical science behind these recent breakthroughs in tr-ARPES and recent results from my lab regarding graphene and monolayer WS2, 2D materials being used now in optoelectronic devices. Direct visualization of momentum-space wave functions enables the study of light-matter interaction with an unprecedented level of detail, with new discoveries unseen in previous measurements. 

Speaker Bio(s): 

Thomas Allison is an associate professor of both Physics and Chemistry at Stony Brook University. He earned his undergraduate degree in Engineering Physics at Cornell University and his Ph. D. in Physics at the University of California, Berkeley. Allison has been awarded the Dept. of Energy Early Career Award and been named an Air Force Office of Scientific Research Young Investigator. He was also the winner of the 2017 Stony Brook Foundation Discovery Prize. Prof. Allison’s current research applies frequency combs to ultrafast and nonlinear spectroscopy.