Observation of Rapid Exciton–Exciton Annihilation in Monolayer Molybdenum Disulfide

Sun, Dezheng; Rao, Yi; Reider, Georg A.; Chen, Gugang; You, Yu‐Meng; Brézin, Louis; Harutyunyan, Avetik R.; Heinz, Tony F.

doi:10.1021/nl5021975

Cited by 518 publications

(629 citation statements)

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“…This means the actual exciton density (n) may be slightly smaller than the excitation density (n 0 ). During this process, exciton-exciton annihilation could happen with a decay rate that depends on the initial excitation density, as studied by Sun et al 49 and Kumar et al 50 . We incorporated this process in our analysis, and used the obtained time-delayed density n(t) in our main text n(t) = n 0 (1 + k A n 0 t)…”

Section: Appendix C: Intravalley Electron Spin Reversalmentioning

confidence: 99%

“…where η (= 5%) is the laser fluence fluctuation and ∆k A (= 1.1 × 10 −2 cm 2 /s, 49 ) is the standard deviation of the exciton-exciton annihilation rate. In order to determine the correct power-law behavior, we plot the results with three different exponents of k = 1/2, 3/4, 1 and make a comparison through a linear fitting of the first seven data points (Fig E1).…”

Section: Appendix C: Intravalley Electron Spin Reversalmentioning

confidence: 99%

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Intervalley biexcitons and many-body effects in monolayerMoS2

et al. 2015

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Interactions between two excitons can result in the formation of bound quasiparticles, known as biexcitons. Their properties are determined by the constituent excitons, with orbital and spin states resembling those of atoms. Monolayer transition metal dichalcogenides (TMDs) present a unique system where excitons acquire a new degree of freedom, the valley pseudospin, from which a novel intervalley biexciton can be created. These biexcitons comprise two excitons from different valleys, which are distinct from biexcitons in conventional semiconductors and have no direct analogue in atomic and molecular systems. However, their valley properties are not accessible to traditional transport and optical measurements. Here, we report the observation of intervalley biexcitons in the monolayer TMD MoS2 using ultrafast pump-probe spectroscopy. By applying broadband probe pulses with different helicities, we identify two species of intervalley biexcitons with large binding energies of 60 meV and 40 meV. In addition, we also reveal effects beyond biexcitonic pairwise interactions in which the exciton energy redshifts at increasing exciton densities, indicating the presence of many-body interactions among them.

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Section: Appendix C: Intravalley Electron Spin Reversalmentioning

confidence: 99%

Section: Appendix C: Intravalley Electron Spin Reversalmentioning

confidence: 99%

Intervalley biexcitons and many-body effects in monolayerMoS2

et al. 2015

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“…5 Calculations predict a room temperature lifetime in the range of hundreds of picoseconds, 14,15 in agreement with some experiments. 16,17 However, many processes can obscure the actual radiative lifetime, such as defect-mediated non-radiative decay, 18 exciton-exciton interactions, 19 or equilibration with dark states. 20 Here we show that the long apparent lifetime in acid-treated MoS 2 is due to the presence of long-lived (4 µs) dark states that extend hundreds of meV into the bandgap.…”

Section: -11mentioning

confidence: 99%

Exciton trapping is responsible for the long apparent lifetime in acid-treated MoS2

2017

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Here, we show that deep trapped "dark" exciton states are responsible for the surprisingly long lifetime of band-edge photoluminescence in acid-treated single-layer MoS 2 . Temperaturedependent transient photoluminescence spectroscopy reveals an exponential tail of long-lived states extending hundreds of meV into the band gap. These sub-band states, which are characterized by a 4 µs radiative lifetime, quickly capture and store photogenerated excitons before subsequent thermalization up to the band edge where fast radiative recombination occurs. By intentionally saturating these trap states, we are able to measure the "true" 150 ps radiative lifetime of the band-edge exciton at 77 K, which extrapolates to ∼600 ps at room temperature. These experiments reveal the dominant role of dark exciton states in acid-treated MoS 2 , and suggest that excitons spend > 95% of their lifetime at room temperature in trap states below the band edge. We hypothesize that these states are associated with native structural defects, which are not introduced by the superacid treatment; rather, the superacid treatment dramatically reduces non-radiative recombination through these states, extending the exciton lifetime and increasing the likelihood of eventual radiative recombination.

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“…The capture rates which display both linear and quadratic dependences on the exciton density arises primarily from the large overlap of the defect state wavefunction with the conduction or valence band Bloch state wavefunctions. The exciton capture rates are almost comparable to the exciton-exciton annihilation (EEA) rates 8,30 that becomes dominant as a result of the reduced Coulomb screening of spatially confined charge carriers in layered transition metal dichalcogenides.…”

Section: Introductionmentioning

confidence: 98%

Ultrafast exciton relaxation in monolayer transition metal dichalcogenides

Thilagam

2016

Journal of Applied Physics

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We examine a mechanism by which excitons undergo ultrafast relaxation in common monolayer transition metal dichalcogenides. It is shown that at densities ≈ 1× 10 11 cm −2 and temperatures ≤ 60 K, excitons in well known monolayers (MoS2, MoSe2, WS2 and WSe2) exist as point-like structureless electron-hole quasiparticles. We evaluate the average rate of exciton energy relaxation due to acoustic phonons via the deformation potential and the piezoelectric coupling mechanisms and examine the effect of spreading of the excitonic wavefunction into the region perpendicular to the monolayer plane. Our results show that the exciton relaxation rate is enhanced with increase in the exciton temperature, while it is decreased with increase in the lattice temperature. Good agreements with available experimental data are obtained when the calculations are extrapolated to room temperatures. A unified approach taking into account the deformation potential and piezoelectric coupling mechanisms shows that exciton relaxation induced by phonons is as significant as defect assisted scattering and trapping of excitons by surface states in monolayer transition metal dichalcogenides.

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Observation of Rapid Exciton–Exciton Annihilation in Monolayer Molybdenum Disulfide

Cited by 518 publications

References 41 publications

Intervalley biexcitons and many-body effects in monolayerMoS2

Intervalley biexcitons and many-body effects in monolayerMoS2

Exciton trapping is responsible for the long apparent lifetime in acid-treated MoS2

Ultrafast exciton relaxation in monolayer transition metal dichalcogenides

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