Probing and Controlling Excitons in 2D Semiconductors and Heterostructures

Van Hove Charge Density Waves on Hexagonal Lattices and Kagome Superconductors
November 18, 2022

Monday, November 21, 2022 from 2:30-3:30 p.m.
Location: 325 Physics South Hall & Zoom
Speaker: Tony F. Heinz, Stanford University

Abstract:One of the key features of the optical response of 2D semiconductors is the dominant role of excitonic interactions. The strong influence of these many-body effects reflects the reduced dimensionality combined with the reduced dielectric screening of atomically thin crystals. In our talk, we will review progress in understanding the nature of optically excited states in 2D monolayers and heterostructures. We will describe how excitonic states can be tuned and probed be altering the Coulomb interaction within the layer by various approaches, including through changes in the external dielectric environment. We will particularly emphasize recent advances in applying time-resolved ARPES (angularly resolved photoemission spectroscopy) to examine the momentum-space character and dynamics of excitons in transition metal dichalcogenide semiconductors. In these studies, carried out in collaboration with the group of Keshav Dani, we have been able not only to determine the valley characteristics of both bright and dark excitons, but also to image the wavefunction of excitonic states in momentum space.

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