Dark excitons in transition metal dichalcogenides

Abstract

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.

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Cited by in corpus (18)

• Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe2/MoSe2 Heterostructure
• Multipath optical recombination of intervalley dark excitons and trions in monolayer WSe${}_2$
• Exciton optics, dynamics and transport in atomically thin semiconductors
• Nonclassical Exciton Diffusion in Monolayer WSe2
• Dark-exciton driven energy funneling into dielectric inhomogeneities in two-dimensional semiconductors
• Delocalization of dark and bright excitons in flat-band materials and the optical properties of V${}_2$O${}_5$
• Visualization of dark excitons in semiconductor monolayers for high-sensitivity strain sensing
• Direct Observation of Intravalley Phonon Scattering of 2s Excitons in MoSe${}_2$ and WSe${}_2$ Monolayers
• Moiré Engineering of Spin-Orbit Coupling in Twisted Platinum Diselenide
• Light-matter coupling and non-equilibrium dynamics of exchange-split trions in monolayer WS2
• Monolayer Semiconductor Auger Detector
• Magnetic field mixing and splitting of bright and dark excitons in monolayer MoSe2
• Molecule signatures in photoluminescence spectra of transition metal dichalcogenides
• Hybrid dark excitons in monolayer ${MoS}_2$
• Spectral asymmetry of phonon sideband luminescence in monolayer and bilayer WSe2
• Dark-Exciton-Mediated Fano Resonance from a Single Gold Nanostructure Deposited on Monolayer WS2 at Room Temperature
• Strong Interaction of Cherenkov Radiation with Excitons in WSe2 Crystals
• Radiative Decay of Dark Exciton Related Emission in a Sandwiched Monolayer WSe2 Revealed by Room Temperature Micro and Nano Photoluminescence