Directly visualizing the momentum-forbidden dark excitons and their dynamics in atomically thin semiconductors
Year: 2020
Type: article
Abstract: Resolving momentum degrees of freedom of excitons, which are electron-hole pairs bound by the Coulomb attraction in a photoexcited semiconductor, has remained an elusive goal for decades. In atomically thin semiconductors, such a capability could probe the momentum-forbidden dark excitons, which critically affect proposed opto-electronic technologies but are not directly accessible using optical techniques. Here, we probed the momentum state of excitons in a tungsten diselenide monolayer by photoemitting their constituent electrons and resolving them in time, momentum, and energy. We obtained a direct visual of the momentum-forbidden dark excitons and studied their properties, including their near degeneracy with bright excitons and their formation pathways in the energy-momentum landscape. These dark excitons dominated the excited-state distribution, a surprising finding that highlights their importance in atomically thin semiconductors.
Source: Science
Authors: Julien Madéo, Michael K. L. Man, Chakradhar Sahoo, Marshall Campbell, Vivek Pareek, E. Laine Wong, Abdullah Al-Mahboob, Nicholas S. Chan, Arka Karmakar, Bala Murali Krishna Mariserla, Xiaoqin Li, Tony F. Heinz, Ting Cao, Keshav M. Dani
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, Micron Foundation, University of Washington, Okinawa Institute of Science and Technology Graduate University, Materials Research Science and Engineering Center, Harvard University, Japan Society for the Promotion of Science, National Science Foundation of Sri Lanka, Division of Materials Research, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, SLAC National Accelerator Laboratory
Awards: G1286251239, G1301677854, G1372744343, G1500824199, G303061748, G3871488735, G4285111415, G4817264520, Center for Dynamics and Control of Materials, G5412571837, G6139170584, G6725192607, XSEDE: eXtreme Science and Engineering Discovery Environment, G7070193645, G7088042312, Understanding the interactions and emerging new properties in two-dimensional heterostructures, MRSEC: UW Molecular Engineering Materials Center, G911061179, G969889393
OpenAlex ID: W3022228887