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Dark trions and biexcitons in WS 2 and WSe 2 made bright by e-e scattering

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ABSTRACT

The direct band gap character and large spin-orbit splitting of the valence band edges (at the K and K’ valleys) in monolayer transition metal dichalcogenides have put these two-dimensional materials under the spot-light of intense experimental and theoretical studies. In particular, for Tungsten dichalcogenides it has been found that the sign of spin splitting of conduction band edges makes ground state excitons radiatively inactive (dark) due to spin and momentum mismatch between the constituent electron and hole. One might similarly assume that the ground states of charged excitons and biexcitons in these monolayers are also dark. Here, we show that the intervalley (K ⇆ K′) electron-electron scattering mixes bright and dark states of these complexes, and estimate the radiative lifetimes in the ground states of these “semi-dark” trions and biexcitons to be ~10 ps, and analyse how these complexes appear in the temperature-dependent photoluminescence spectra of WS2 and WSe2 monolayers.

No MeSH data available.


Low temperature photoluminescence spectrum of WX2.Sketch of the low temperature (kBT < ΔSO) photoluminescence spectrum of WX2 including the bright exciton, dark and bright trions (green) and dark and bright biexcitons (red). The excited bright trions and excitons are denoted by T* and B*. The dark exciton (Xd) energy is marked as a reference point .
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f2: Low temperature photoluminescence spectrum of WX2.Sketch of the low temperature (kBT < ΔSO) photoluminescence spectrum of WX2 including the bright exciton, dark and bright trions (green) and dark and bright biexcitons (red). The excited bright trions and excitons are denoted by T* and B*. The dark exciton (Xd) energy is marked as a reference point .

Mentions: The mixing of the dark and bright states produces photoluminescence lines shown schematically in Fig. 2. The emitted photon energies of these lines are determined by both the binding energies and the shake-up into the higher-energy spin-split c-band in the final state,


Dark trions and biexcitons in WS 2 and WSe 2 made bright by e-e scattering
Low temperature photoluminescence spectrum of WX2.Sketch of the low temperature (kBT < ΔSO) photoluminescence spectrum of WX2 including the bright exciton, dark and bright trions (green) and dark and bright biexcitons (red). The excited bright trions and excitons are denoted by T* and B*. The dark exciton (Xd) energy is marked as a reference point .
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382684&req=5

f2: Low temperature photoluminescence spectrum of WX2.Sketch of the low temperature (kBT < ΔSO) photoluminescence spectrum of WX2 including the bright exciton, dark and bright trions (green) and dark and bright biexcitons (red). The excited bright trions and excitons are denoted by T* and B*. The dark exciton (Xd) energy is marked as a reference point .
Mentions: The mixing of the dark and bright states produces photoluminescence lines shown schematically in Fig. 2. The emitted photon energies of these lines are determined by both the binding energies and the shake-up into the higher-energy spin-split c-band in the final state,

View Article: PubMed Central - PubMed

ABSTRACT

The direct band gap character and large spin-orbit splitting of the valence band edges (at the K and K&rsquo; valleys) in monolayer transition metal dichalcogenides have put these two-dimensional materials under the spot-light of intense experimental and theoretical studies. In particular, for Tungsten dichalcogenides it has been found that the sign of spin splitting of conduction band edges makes ground state excitons radiatively inactive (dark) due to spin and momentum mismatch between the constituent electron and hole. One might similarly assume that the ground states of charged excitons and biexcitons in these monolayers are also dark. Here, we show that the intervalley (K&thinsp;&#8646;&thinsp;K&prime;) electron-electron scattering mixes bright and dark states of these complexes, and estimate the radiative lifetimes in the ground states of these &ldquo;semi-dark&rdquo; trions and biexcitons to be ~10&thinsp;ps, and analyse how these complexes appear in the temperature-dependent photoluminescence spectra of WS2 and WSe2 monolayers.

No MeSH data available.