Dark excitons in transition metal dichalcogenides
Journal article, 2018

Monolayer transition metal dichalcogenides (TMDs) exhibit a remarkably strong Coulomb interaction that manifests in tightly bound excitons. Due to the complex electronic band structure exhibiting several spin-split valleys in the conduction and valence band, dark excitonic states can be formed. They are inaccessibly by light due to the required spin-flip and/or momentum transfer. The relative position of these dark states with respect to the optically accessible bright excitons has a crucial impact on the emission efficiency of these materials and thus on their technological potential. Based on the solution of the Wannier equation, we present the excitonic landscape of the most studied TMD materials including the spectral position of momentum- and spin-forbidden excitonic states. We show that the knowledge of the electronic dispersion does not allow to conclude about the nature of the material's band gap since excitonic effects can give rise to significant changes. Furthermore, we reveal that an exponentially reduced photoluminescence yield does not necessarily reflect a transition from a direct to a nondirect gap material, but can be ascribed in most cases to a change of the relative spectral distance between bright and dark excitonic states.

Author

Ermin Malic

Chalmers, Physics, Condensed Matter Theory

Malte Selig

Technische Universität Berlin

Maja Feierabend

Chalmers, Physics, Condensed Matter Theory

Samuel Brem

Chalmers, Physics, Condensed Matter Theory

Dominik Christiansen

Technische Universität Berlin

Florian Wendler

Technische Universität Berlin

Andreas Knorr

Technische Universität Berlin

Gunnar Berghäuser

Chalmers, Physics, Condensed Matter Theory

Physical Review Materials

2475-9953 (ISSN)

Vol. 2 1 014002

Graphene Core1. Graphene-based disruptive technologies (Graphene Flagship)

European Commission (Horizon 2020), 2016-04-01 -- 2018-03-31.

Subject Categories

Atom and Molecular Physics and Optics

Condensed Matter Physics

DOI

10.1103/PhysRevMaterials.2.014002

More information

Latest update

1/25/2019