Role of Nonequilibrium Populations in Dark-Exciton Formation
Journal article, 2026
The optical excitation of a bright exciton may be followed by the formation of lower-energy dark states. In these formation and relaxation processes, nonequilibrium exciton and phonon populations play a dominant role but remain so far largely unexplored, as most states are inaccessible by regular spectroscopies. Here, on the example of homobilayer 2H-MoS2, we realize direct access to the full exciton relaxation cascade from experiment and theory. We find distinct changes in the time-, energy-, and in-plane momentum-resolved photoemission spectral function that can be explained only when considering the formation and subsequent thermalization of excitonic nonequilibrium occupation distributions. In agreement with microscopic many-particle calculations, we quantify the timescales for the formation of a nonequilibrium dark-excitonic occupation and its subsequent thermalization to 85 and 150 fs, respectively. Our results provide a previously inaccessible view of the complete exciton relaxation cascade, which is of importance for the future characterization of nonequilibrium excitonic phases and the efficient design of optoelectronic devices.
Author
Paul Werner
University of Göttingen
Wiebke Bennecke
University of Göttingen
Jan Philipp Bange
University of Göttingen
Giuseppe Meneghini
Philipps University Marburg
David Schmitt
University of Göttingen
Marco Merboldt
University of Göttingen
Anna M. Seiler
University of Göttingen
Abdul Aziz AlMutairi
University of Cambridge
King Fahd University of Petroleum and Minerals
Kenji Watanabe
National Institute for Materials Science (NIMS)
Takashi Taniguchi
National Institute for Materials Science (NIMS)
G. S.Matthijs Jansen
University of Göttingen
Junde Liu
University of Göttingen
Daniel Steil
University of Göttingen
Stephan Hofmann
University of Cambridge
R. Thomas Weitz
University of Göttingen
Ermin Malic
Chalmers, Physics, Condensed Matter and Materials Theory
Philipps University Marburg
Stefan Mathias
University of Göttingen
Marcel Reutzel
University of Göttingen
Philipps University Marburg
Physical Review Letters
0031-9007 (ISSN) 1079-7114 (eISSN)
Vol. 136 18 186903Subject Categories (SSIF 2025)
Condensed Matter Physics
Other Physics Topics
DOI
10.1103/w29j-z48v
PubMed
42172393