Energy Spectrum of Two-Dimensional Excitons in a Nonuniform Dielectric Medium

Molas, Maciej R.; Slobodeniuk, A. O.; Nogajewski, Karol; Bartoš, Miroslav; Bala, Łukasz; Babiński, A.; Watanabe, Kenji; Taniguchi, Takashi; Faugeras, C.; Potemski, M.

doi:10.1103/physrevlett.123.136801

Cited by 70 publications

(108 citation statements)

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“…As the technique is background free and detection is at the shot-noise limit, apart from 1S and 2S states, FWM reveals further resonances attributed to 3S and 4S states. When plotting the energy versus the quantum number (see inset) we observe non-hydrogenic series, in line with previous findings [12] and the EX binding energy [13,14] of E b =161 meV. D. Exciton coherence dynamics in the WSe2 heterostructue: dephasing and coherent coupling FWM transients versus τ 12 measured for 1S and 2S states are shown as color maps in Fig.…”

Section: Reflectance and Fwm Response In A Wse2 Heterostructuresupporting

confidence: 89%

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Coherent dynamics and mapping of excitons in single-layer MoSe2 and WSe2 at the homogeneous limit

Boule¹,

Václavková²,

Bartoš³

et al. 2020

Phys. Rev. Materials

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We perform coherent nonlinear spectroscopy of excitons in single-layers of MoSe2 and WSe2 encapsulated between thin films of hexagonal boron nitride. Employing four-wave mixing microscopy we identify virtually disorder free areas, generating exciton optical response at the homogeneous limit. Focussing on such areas, we measure exciton homogeneous broadening as a function of environmental factors, namely temperature and exciton density. Exploiting FWM imaging, we find that at such locations, nonlinear absorption of the exciton excited states and their coherent couplings can be observed. Using the WSe2 heterostructure, we infer coherence and density dynamics of the exciton 2S state. Owing to its increased radiative lifetime, at low temperatures, the dephasing of the 2S state is longer than of the 1S transition. While scanning various heterostructures across tens of micrometers, we conclude that the disorder, principally induced by strain variations, remain to be present creating spatially varying inhomogeneous broadening. arXiv:2002.01436v2 [cond-mat.mtrl-sci]

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Section: Reflectance and Fwm Response In A Wse2 Heterostructuresupporting

confidence: 89%

“…Encapsulation thus yields step-like improvement of optical properties. The main indicator of such improvement was the narrowing of the EX linewidth and appearance of the Rydberg series of the EX's excited states [10,[12][13][14]. coherence coherence Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Coherent dynamics and mapping of excitons in single-layer MoSe2 and WSe2 at the homogeneous limit

Boule¹,

Václavková²,

Bartoš³

et al. 2020

Phys. Rev. Materials

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“…These changes are evidenced in Fig. 2 which shows the PL spectrum after encapsulation (black curve): most noticeable is the linewidth of A exciton 1s peak which is strongly reduced down to 4.7 meV, the resonance corresponding to the exciton 1s peak in reflectance is red shifted by 4 meV as a result of the change in the di- electric properties of the surrounding environment (SiO 2 and vaccuum with respect to h-BN), a new structure is observed at higher energies close to 1.87 eV which we attribute to the 2s excited state of the A exciton 8,9 . Finally, the broad band at lower energy acquires a rich structure of discrete peaks associated to 33 the biexciton XX, the singlet and triplet trions T, possibly the dark exciton, the charged biexciton XX-, and finally to localized excitons L. In Fig.…”

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confidence: 77%

Magneto-spectroscopy of exciton Rydberg states in a CVD grown WSe2 monolayer

Delhomme

Guilliam

Zheng

et al. 2019

Applied Physics Letters

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The results of magneto-optical spectroscopy investigations of excitons in a CVD grown monolayer of WSe 2 encapsulated in hexagonal boron nitride are presented. The emission linewidth for the 1s state is of 4.7 meV, close to the narrowest emissions observed in monolayers exfoliated from bulk material. The 2s excitonic state is also observed at higher energies in the photoluminescence spectrum. Magneto-optical spectroscopy allows for the determination of the g-factors and of the spatial extent of the excitonic wave functions associated with these emissions. Our work establishes CVD grown monolayers of transition metal dichalcogenides as a mature technology for optoelectronic applications.Monolayers of semiconducting transition metal dichalcogenides (S-TMD), labelled as MX 2 , where M=W, Mo, Re or Zr and X=S, Se or Te for the most studied compounds, are direct band gap semiconductors with the band gap located at the two inequivalent K ± points of their hexagonal Brillouin zone 1 . They exhibit a large number of properties interesting both for fundamental science and for technology 2 . These properties include a band gap in the visible range 3 , a strong light matter coupling 4 , the presence of single photon emitters 5,6 , very strong excitonic effects 7-9 , possibilities of tuning the emission energy by Coulomb engineering 10,11 , and the opportunity of combining them to obtain type II band alignment 12 . The spin-orbit interaction in these materials is strong and splits the spin levels in the valence band by few hundreds of meV, and by few tens of meV in the conduction band 13 . This large splitting in the valence band defines two different excitons at the K ± points attached to the two spin-split bands, named A and B excitons 14 . Because of the lack of inversion symmetry, the two different valleys can be excited independently using circularly polarized light 15 , opening the possibility of initializing an exciton population in a given valley, or creating coherent superpositions of both valleys 16 .Best specimens of S-TMD monolayers are usually obtained by the mechanical exfoliation of bulk (natural or synthetic) crystals which leads to micrometer sized flakes, suitable for scientific investigations or for demonstrating a) Electronic mail: clement.faugeras@lncmi.cnrs.fr prototype devices, but preventing their use in realistic applications produced at an industrial scale. Growth techniques, mainly chemical vapor deposition (CVD) 17 and molecular beam epitaxy (MBE) 18,19 , have been developed to produce large scale monolayers of S-TMD suitable for electronics and optoelectronics applications, or to elaborate vertical/horizontal heterostructures 20,21 . In this letter, we demonstrate CVD grown S-TMD monolayers with optical quality comparable to state of the art exfoliated flakes. For that purpose, we have encapsulated it in between hexagonal boron nitride (h-BN) flakes in order to unveil its intrinsic properties. We show that the optical response of this CVD grown monolayer is comparable to the best exfoliated monol...

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“…In the Si-based system considered here, excitons are not expected to play a significant role. However, this is not the case of hybrid interfaces composed of TMDCs, where screening and excitonic effects are known to be very relevant [26,[141][142][143][144][145][146] also in the dynamical regime [147][148][149][150][151][152]. Combined efforts in the aforementioned directions will offer unprecedented insight into the fundamental mechanisms of charge-transfer dynamics in hybrid interfaces, paving the way for controlled manipulation of lightmatter interaction in this class of materials on the atomistic space and time scales.…”

Section: Summary Conclusion and Outlookmentioning

confidence: 99%

Ultrafast charge transfer and vibronic coupling in a laser-excited hybrid inorganic/organic interface

Jacobs

Krumland

Valencia

et al. 2020

Advances in Physics: X

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Hybrid interfaces formed by inorganic semiconductors and organic molecules are intriguing materials for opto-electronics. Interfacial charge transfer is primarily responsible for their peculiar electronic structure and optical response. Hence, it is essential to gain insight into this fundamental process also beyond the static picture. Ab initio methods based on real-time time-dependent density-functional theory coupled to the Ehrenfest molecular dynamics scheme are ideally suited for this problem. We investigate a laser-excited hybrid inorganic/organic interface formed by the electron acceptor molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) physisorbed on a hydrogenated silicon cluster, and we discuss the fundamental mechanisms of charge transfer in the ultrashort time window following the impulsive excitation. The considered interface is p-doped and exhibits charge transfer in the ground state. When it is excited by a resonant laser pulse, the charge transfer across the interface is additionally increased, but contrary to previous observations in allorganic donor/acceptor complexes, it is not further promoted by vibronic coupling. In the considered time window of 100 fs, the molecular vibrations are coupled to the electron dynamics and enhance intramolecular charge transfer. Our results highlight the complexity of the physics involved and demonstrate the ability of the adopted formalism to achieve a comprehensive understanding of ultrafast charge transfer in hybrid materials.

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Energy Spectrum of Two-Dimensional Excitons in a Nonuniform Dielectric Medium

Cited by 70 publications

References 53 publications

Coherent dynamics and mapping of excitons in single-layer MoSe2 and WSe2 at the homogeneous limit

Coherent dynamics and mapping of excitons in single-layer MoSe2 and WSe2 at the homogeneous limit

Magneto-spectroscopy of exciton Rydberg states in a CVD grown WSe2 monolayer

Ultrafast charge transfer and vibronic coupling in a laser-excited hybrid inorganic/organic interface

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