Exciton center-of-mass localization and dielectric environment effect in monolayer WS2

Hichri, A.; Amara, Imen Ben; Ayari, Sabrine; Jaziri, S.

doi:10.1063/1.4984790

Cited by 24 publications

(34 citation statements)

References 88 publications

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“…Assuming disorder centers far away from each other, R 0 only leads to a phase in the momentum space. The approximation of a Gaussian disorder potential is well established in theory [41][42][43] and moreover, experimentally measured potential traps reveal a Gaussian-like behavior [19,22]. Note that our theory is not limited to Gaussian potentials but could be extended to other potential forms, such as elliptical [44] or nanobubbles [45].…”

Section: Theoretical Approachmentioning

confidence: 66%

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Optical fingerprint of bright and dark localized excitonic states in atomically thin 2D materials

Feierabend

Brem

Malić

2019

Phys. Chem. Chem. Phys.

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Point defects, local strain or impurities can crucially impact the optical response of atomically thin twodimensional materials as they offer trapping potentials for excitons. These trapped excitons appear in photoluminescence spectra as new resonances below the bright exciton that can even be exploited for single photon emission. While large progress has been made in deterministically introducing defects, only little is known about their impact on the optical fingerprint of 2D materials. Here, based on a microscopic approach we reveal direct signatures of localized bright excitonic states as well as indirect phonon-assisted side bands of localized momentum-dark excitons. The visibility of localized excitons strongly depends on temperature and disorder potential width. This results in different regimes, where either the bright or dark localized states are dominant in optical spectra. We trace back this behavior to an interplay between disorder-induced exciton capture and intervalley exciton-phonon scattering processes.

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Section: Theoretical Approachmentioning

confidence: 66%

“…By transforming the disorder potential into momentum space we find that it leads to a quantization of the exciton center-of-mass momentum, i.e. excitons cannot move freely anymore [42]. Then, we project the phonon-assisted polarization into a localized excitonic basis with S µ…”

Section: Theoretical Approachmentioning

confidence: 99%

Optical fingerprint of bright and dark localized excitonic states in atomically thin 2D materials

Feierabend

Brem

Malić

2019

Phys. Chem. Chem. Phys.

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“…This assumption can be justified by using the Saha equation. In fact, with respect to the mechanism leading to equilibrium between free excitons n XB free electrons n e , and free holes n h we apply the equilibrium thermal analysis using a Saha equation

\frac{n_{normale} n_{normalh}}{n_{X B}} = \frac{g_{normale} g_{normale}}{g_{X B}} \frac{μ}{2 π ℏ^{2}} e^{\frac{- E_{normalB}}{k_{normalB} T}} = \frac{K_{X B}^{i o n}}{K_{X B}^{normalF}}

…”

Section: Dynamics Of Excitonic States In Transition Metals Dichalcogementioning

confidence: 99%

Dynamics of Free and Localized Excitons in Two‐Dimensional Transition Metal Dichalcogenides

Ayari

Jaziri

2019

Physica Status Solidi (b)

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Exciton kinetics in transition‐metal dichalcogenide materials is highly dependent to the experimental conditions and the quality of the sample. This study presents a comprehensive model comprising a complete set of rate equations, which account for charge transfer among multiexcitonic channels including bright and dark excitons, trions, localized excitons, to investigate the dynamics of excitons in monolayer WSe2. The exciton dynamics involving both intra‐ and intervalley scattering is discussed. In this respect, for high quality samples, it is proved that the kinetics of excitons in darkish materials is dominated by intravalley scattering in which low‐lying optically dark exciton states constitute an important reservoir while in the case of molybdenides only intervalley scattering is efficient. For low quality samples, the dynamics of localized exciton states and negative trion in case of n‐type doping sample is studied. It is shown that localized exciton states decay on a longer time scale than the trion and free exciton, consistent with experimental findings of Wang et al. [Phys. Rev. B 2014, 90, 075413]. Finally, the dependence of the trion and localized exciton dynamics as a function of the electron density is studied. It is found that the trion and localized exciton populations strongly depend to the doping density.

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“…In this case, we can separate the exciton center of mass and relative motion . The Hamiltonian of relative motion is largely studied in previous work [59,67].…”

Section: Description Of the Hamiltonien Of The Localized Exciton Via mentioning

confidence: 99%

“…In the presence of random disorder potential , the momentum of the center-of-mass motion is no longer a good quantum number as was assumed in the previous model related to the free exciton [38,49,59].…”

Section: Description Of the Hamiltonien Of The Localized Exciton Via mentioning

confidence: 99%

Radiative lifetime of localized excitons in transition-metal dichalcogenides

et al. 2018

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Disorder derived from defects or strain in monolayer TMDs can lead to a dramatic change in the physical behavior of the interband excitations, producing inhomogeneous spectral broadening and localization; leading to radiative lifetime increase. In this study, we have modeled the disorder in the surface of the sample through a randomized potential in monolayer WSe2. We show that this model allows us to simulate the spectra of localized exciton states as well as their radiative lifetime. In this context, we give an in depth study of the influence of the disorder potential parameters on the optical properties of these defects through energies, density of states, oscillator strengths, photoluminescence (PL) spectroscopy and radiative lifetime at low temperature (4K).We demonstrate that localized excitons have a longer emission time than free excitons, in the range of tens of picoseconds or more, and we show that it depends strongly on the disorder parameter and dielectric environment. Finally, in order to prove the validity of our model we compare it to available experimental results of the literature.

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Exciton center-of-mass localization and dielectric environment effect in monolayer WS2

Cited by 24 publications

References 88 publications

Optical fingerprint of bright and dark localized excitonic states in atomically thin 2D materials

Optical fingerprint of bright and dark localized excitonic states in atomically thin 2D materials

Dynamics of Free and Localized Excitons in Two‐Dimensional Transition Metal Dichalcogenides

Radiative lifetime of localized excitons in transition-metal dichalcogenides

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