Dark excitons in transition metal dichalcogenides
Autor: | Gunnar Berghäuser, Maja Feierabend, Andreas Knorr, Dominik Christiansen, Ermin Malic, Samuel Brem, Florian Wendler, Malte Selig |
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Rok vydání: | 2018 |
Předmět: |
Condensed Matter - Materials Science
Photoluminescence Materials science Physics and Astronomy (miscellaneous) Condensed matter physics Band gap Atom and Molecular Physics and Optics Exciton Momentum transfer Materials Science (cond-mat.mtrl-sci) FOS: Physical sciences Wannier equation 02 engineering and technology Condensed Matter Physics Condensed Matter::Mesoscopic Systems and Quantum Hall Effect 021001 nanoscience & nanotechnology 01 natural sciences Momentum Condensed Matter::Materials Science 0103 physical sciences Coulomb General Materials Science 010306 general physics 0210 nano-technology Electronic band structure |
Zdroj: | Physical Review Materials Physical Review Materials vol.2(2018) |
ISSN: | 2475-9953 |
DOI: | 10.1103/PhysRevMaterials.2.014002 |
Popis: | 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 non-direct gap material, but can be ascribed in most cases to a change of the relative spectral distance between bright and dark excitonic states. |
Databáze: | OpenAIRE |
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