Non-equilibrium diffusion of dark excitons in atomically thin semiconductors
Journal article, 2021
Atomically thin semiconductors provide an excellent platform to study intriguing many-particle physics of tightly-bound excitons. In particular, the properties of tungsten-based transition metal dichalcogenides are determined by a complex manifold of bright and dark exciton states. While dark excitons are known to dominate the relaxation dynamics and low-temperature photoluminescence, their impact on the spatial propagation of excitons has remained elusive. In our joint theory-experiment study, we address this intriguing regime of dark state transport by resolving the spatio-temporal exciton dynamics in hBN-encapsulated WSe2 monolayers after resonant excitation. We find clear evidence of an unconventional, time-dependent diffusion during the first tens of picoseconds, exhibiting strong deviation from the steady-state propagation. Dark exciton states are initially populated by phonon emission from the bright states, resulting in creation of hot (unequilibrated) excitons whose rapid expansion leads to a transient increase of the diffusion coefficient by more than one order of magnitude. These findings are relevant for both fundamental understanding of the spatio-temporal exciton dynamics in atomically thin materials as well as their technological application by enabling rapid diffusion.
Author
Roberto Rosati
Philipps University Marburg
Koloman Wagner
Technische Universität Dresden
University of Regensburg
Samuel Brem
Philipps University Marburg
Raul Perea Causin
Chalmers, Physics, Condensed Matter and Materials Theory
Jonas D. Ziegler
University of Regensburg
Technische Universität Dresden
Jonas Zipfel
University of Regensburg
Lawrence Berkeley National Laboratory
Takashi Taniguchi
National Institute for Materials Science (NIMS)
Kenji Watanabe
National Institute for Materials Science (NIMS)
Alexey Chernikov
Technische Universität Dresden
University of Regensburg
Ermin Malic
Philipps University Marburg
Chalmers, Physics, Condensed Matter and Materials Theory
Nanoscale
2040-3364 (ISSN)
Vol. 13 47 19966-19972Graphene Core Project 3 (Graphene Flagship)
European Commission (EC) (EC/H2020/881603), 2020-04-01 -- 2023-03-31.
Subject Categories
Atom and Molecular Physics and Optics
Other Physics Topics
Condensed Matter Physics
DOI
10.1039/d1nr06230a
PubMed
34821228