Exciton valley dynamics probed by Kerr rotation in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">WSe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>monolayers

Zhu, Chao; Zhang, K.; Glazov, M. M.; Urbaszek, B.; Amand, T.; Ji, Zhurun; Liu, Baoli; Marie, X.

doi:10.1103/physrevb.90.161302

Cited by 288 publications

(328 citation statements)

References 38 publications

(65 reference statements)

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“…This process can be mediated by flexural phonons 23 , and it can occur during the pump pulse duration (Appendix C). On the other hand, the bleaching peaks that are observed using the opposite probe helicity can be explained by intervalley scattering, which is expected to be very fast due to electron-hole exchange interaction in this material 22,24,25 . In particular, valley excitons with finite in-plane momentum can have exchange interaction that generates an inplane effective magnetic field, around which the exciton pseudospin precesses from K to K valley.…”

Section: A Intervalley Biexcitonsmentioning

confidence: 99%

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: A Intervalley Biexcitonsmentioning

confidence: 99%

Intervalley biexcitons and many-body effects in monolayerMoS2

et al. 2015

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“…12,13 Electrons and holes in these materials can form excitons with unusually large binding energies of many hundreds of millielectronvolts, 14−19 making these quasiparticles stable even at elevated temperatures and high carrier densities. 20,21 The properties of excitons in 2D TMDCs are a topic of intense research, investigating, for example, rapid exciton−exciton scattering, 22 interlayer excitons, 23 charged excitons and excitonic molecules, 24,25 ultrafast recombination dynamics, 19,26−28 or efficient coupling to light and lattice vibrations. 4,19,29,30 In many experiments, excitons are created indirectly through nonresonant optical excitation or electronic injection, which may prepare unbound charge carriers with energies far above the exciton resonance.…”

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confidence: 99%

Direct Observation of Ultrafast Exciton Formation in a Monolayer of WSe₂

et al. 2017

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Many of the fundamental optical and electronic properties of atomically thin transition metal dichalcogenides are dominated by strong Coulomb interactions between electrons and holes, forming tightly bound atom-like states called excitons. Here, we directly trace the ultrafast formation of excitons by monitoring the absolute densities of bound and unbound electron−hole pairs in single monolayers of WSe 2 on a diamond substrate following femtosecond nonresonant optical excitation. To this end, phaselocked mid-infrared probe pulses and field-sensitive electro-optic sampling are used to map out the full complex-valued optical conductivity of the nonequilibrium system and to discern the hallmark low-energy responses of bound and unbound pairs. While the spectral shape of the infrared response immediately after above-bandgap injection is dominated by free charge carriers, up to 60% of the electron−hole pairs are bound into excitons already on a subpicosecond time scale, evidencing extremely fast and efficient exciton formation. During the subsequent recombination phase, we still find a large density of free carriers in addition to excitons, indicating a nonequilibrium state of the photoexcited electron−hole system. KEYWORDS: Dichalcogenides, atomically thin 2D crystals, exciton formation, ultrafast dynamics A tomically thin transition metal dichalcogenides (TMDCs) have attracted tremendous attention due to their direct bandgaps in the visible spectral range, 1,2 strong interband optical absorption, 3,4 intriguing spin-valley physics, 5−7 and applications as optoelectronic devices. 8−11 The physics of twodimensional (2D) TMDCs are governed by strong Coulomb interactions owing to the strict quantum confinement in the out-of-plane direction and the weak dielectric screening of the environment. 12,13 Electrons and holes in these materials can form excitons with unusually large binding energies of many hundreds of millielectronvolts, 14−19 making these quasiparticles stable even at elevated temperatures and high carrier densities. 20,21 The properties of excitons in 2D TMDCs are a topic of intense research, investigating, for example, rapid exciton−exciton scattering, 22 interlayer excitons, 23 charged excitons and excitonic molecules, 24,25 ultrafast recombination dynamics, 19,26−28 or efficient coupling to light and lattice vibrations. 4,19,29,30 In many experiments, excitons are created indirectly through nonresonant optical excitation or electronic injection, which may prepare unbound charge carriers with energies far above the exciton resonance. 8,18 Subsequently, the electrons and holes are expected to relax toward their respective band minima and form excitons in the vicinity of the fundamental energy gap. In principle, strong Coulomb attraction in 2D TMDCs should foster rapid exciton formation. Recent optical pump−probe studies relying on interband transitions have reported characteristic formation times on subpicosecond time-scales. 31 The relaxation of large excess energies, however, requires many sca...

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“…[13][14][15] Instead, typical PL peaks of the 2D neutral exciton (2D-X 0 ), 2D charge exciton (2D-X -) and defect-related L exciton band are observed at zero pressure, as shown in Fig. 1 (sample 1).…”

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Single photon emission from deep-level defects in monolayerWSe2

Dou

Ding

et al. 2017

Phys. Rev. B

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We report an efficient method to observe single photon emissions in monolayer WSe 2 by applying hydrostatic pressure. The photoluminescence peaks of typical two-dimensional (2D) excitons show a nearly identical pressure-induced blue-shift, whereas the energy of pressureinduced discrete emission lines (quantum emitters) demonstrates a pressure insensitive behavior.The decay time of these discrete line emissions is approximately 10 ns, which is at least one order longer than the lifetime of the broad localized (L) excitons. These characteristics lead to a conclusion that the excitons bound to deep level defects can be responsible for the observed single photon emissions.

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Exciton valley dynamics probed by Kerr rotation inWSe2monolayers

Cited by 288 publications

References 38 publications

Intervalley biexcitons and many-body effects in monolayerMoS2

Intervalley biexcitons and many-body effects in monolayerMoS2

Direct Observation of Ultrafast Exciton Formation in a Monolayer of WSe₂

Single photon emission from deep-level defects in monolayerWSe2

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Exciton valley dynamics probed by Kerr rotation inWSe2monolayers

Cited by 288 publications

References 38 publications

Intervalley biexcitons and many-body effects in monolayerMoS2

Intervalley biexcitons and many-body effects in monolayerMoS2

Direct Observation of Ultrafast Exciton Formation in a Monolayer of WSe2

Single photon emission from deep-level defects in monolayerWSe2

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Direct Observation of Ultrafast Exciton Formation in a Monolayer of WSe₂