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

2D-Tech

Chalmers, Physics, Condensed Matter and Materials Theory

Jonas D. Ziegler

Technische Universität Dresden

University of Regensburg

Jonas Zipfel

Lawrence Berkeley National Laboratory

University of Regensburg

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

Chalmers, Physics, Condensed Matter and Materials Theory

2D-Tech

Philipps University Marburg

Nanoscale

2040-3364 (ISSN) 2040-3372 (eISSN)

Vol. 13 47 19966-19972

2D material-based technology for industrial applications (2D-TECH)

VINNOVA (2019-00068), 2020-05-01 -- 2024-12-31.

GKN Aerospace Sweden (2D-tech), 2021-01-01 -- 2024-12-31.

Graphene 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

More information

Latest update

2/29/2024