Emerging photoluminescence from the dark-exciton phonon replica in monolayer WSe2

Li, Zhipeng; Wang, Tianmeng; Choi, Jin; Lu, Zhengguang; Lian, Zhongxu; Meng, Yuze; Blei, Mark; Gao, Shiyuan; Taniguchi, Takashi; Ren, Tianhui; Tongay, Sefaattin; Yang, Li; Smirnov, Alexander; Cao, Ting; Shi, Su‐Fei

doi:10.1038/s41467-019-10477-6

Cited by 133 publications

(183 citation statements)

References 55 publications

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“…These phonons have been predicted to play an important role in spin and valley pseudospin relaxation through phononassisted intervalley scattering 7,8 . Additionally, valley phonons can possess chirality with intrinsic pseudo-angular momentum 9 , which has recently attracted wide attention [10][11][12][13] . Such chiral phonons have nontrivial Berry curvature and are predicted to give rise to valley phonon Hall effect, a counterpart of valley Hall effect of electrons in 2D semiconductors [14][15][16] .…”

Section: Maintextmentioning

confidence: 99%

“…Similarly, we can calculate that the effective g-factor is 2(αc-αv-4). The corresponding 0 , + and − states have an effective g-factor close to -9 [7][8][9] . Finally, the intervalley recombination refers to recombination of an electron and a missing electron (hole) in the opposite valleys, but with the same spin quantum number.…”

Section: Si-3 Landé Effective G-factor Analysismentioning

confidence: 99%

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Valley phonons and exciton complexes in a monolayer semiconductor

et al. 2020

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The coupling between spin, charge, and lattice degrees of freedom plays an important role in a wide range of fundamental phenomena. Monolayer semiconducting transitional metal dichalcogenides have emerged as an outstanding platform for studying these coupling effects because they possess unique spin-valley locking physics for hosting rich excitonic species and the reduced screening for strong Coulomb interactions. Here, we report the observation of multiple valley phononsphonons with momentum vectors pointing to the corners of the hexagonal Brillouin zoneand the resulting exciton complexes in the monolayer semiconductor WSe2. From Landé g-factor and polarization analyses of photoluminescence peaks, we find that these valley phonons lead to efficient intervalley scattering of quasi particles in both exciton formation and relaxation. This leads to a series of photoluminescence peaks as valley phonon replicas of dark trions. Using identified valley phonons, we also uncovered an intervalley exciton near charge neutrality, and extract its short-range electron-hole exchange interaction to be about 10 meV. Our work not only identifies a number of previously unknown 2D excitonic species, but also shows that monolayer WSe2 is a prime candidate for studying interactions between spin, pseudospin, and zone-edge phonons.

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Section: Maintextmentioning

confidence: 99%

Section: Si-3 Landé Effective G-factor Analysismentioning

confidence: 99%

Valley phonons and exciton complexes in a monolayer semiconductor

et al. 2020

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“…Finally, we transferred another few-layer graphene flake to work as the top-gate electrode, on top of the top h-BN flake. 26,27 We applied a confocal micro-PL setup to measure the magneto-PL with the out-of-plane magnetic field. A linear polarized light is converted into circularly polarized light by a quarter waveplate and the laser is focused by a 50X objective (NA: ~ 0.65) to excite the WSe2 sample, with the spot size of ~ 2 μm.…”

Section: Fabrication Of H-bn Encapsulated Monolayer Wse2 Devicementioning

confidence: 99%

Momentum-Dark Intervalley Exciton in Monolayer Tungsten Diselenide Brightened via Chiral Phonon

Wang

Choi

et al. 2019

ACS Nano

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Inversion symmetry breaking and three-fold rotation symmetry grant the valley degree of freedom to the robust exciton in monolayer transition metal dichalcogenides (TMDCs), which can be exploited for valleytronics applications. However, the short lifetime of the exciton significantly constrains the possible applications. In contrast, dark exciton could be long-lived but does not necessarily possess the valley degree of freedom. In this work, we report the identification of the momentum-dark, intervalley exciton in monolayer WSe2 through low-temperature magnetophotoluminescence (PL) spectra. Interestingly, the intervalley exciton is brightened through the emission of a chiral phonon at the corners of the Brillouin zone (K point), and the pseudoangular momentum (PAM) of the phonon is transferred to the emitted photon to preserve the valley information. The chiral phonon energy is determined to be ~ 23 meV, based on the experimentally extracted exchange interaction (~ 7 meV), in excellent agreement with the theoretical expectation of 24.6 meV. The long-lived intervalley exciton with valley degree of freedom adds an exciting quasiparticle for valleytronics, and the coupling between the chiral phonon and intervalley exciton furnishes a venue for valley spin manipulation. KEYWORDS: intervalley exciton, chiral phonon, magneto-PL, time-resolved PL, tungsten diselenidethe lifetime of different excitonic complexes by a single exponential function = Ae −t/τ convolved with the response of the laser as a kernel.

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“…Finally, the well-resolved different excitonic peaks allow us to reveal the dynamics of the positive dark trion through time-resolved PL (TRPL) measurement directly 42 . Fig.…”

Section: Main Textmentioning

confidence: 99%

Direct Observation of Gate-Tunable Dark Trions in Monolayer WSe₂

Wang

et al. 2019

Nano Lett.

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Spin-forbidden intravalley dark exciton in tungsten-based transition metal dichalcogenides (TMDCs), owing to its unique spin texture and long lifetime, has attracted intense research interest. Here, we show that we can control the dark exciton electrostatically by dressing it with one free electron or free hole, forming the dark trions. The existence of the dark trions is suggested by the unique magneto-photoluminescence spectroscopy pattern of the boron nitride (BN) encapsulated monolayer WSe2 device at low temperature. The unambiguous evidence of the dark trions is further obtained by directly resolving the radiation pattern of the dark trions through back focal plane imaging. The dark trions possess binding energy of ~ 15 meV, and they inherit the long lifetime and large g-factor from the dark exciton. Interestingly, under the out-of-plane magnetic field, dressing the dark exciton with one free electron or hole results in distinctively different valley polarization of the emitted photon, a result of the different intervalley scattering mechanism for the electron and hole. Finally, the lifetime of the positive dark trion can be further tuned from ~ 50 ps to ~ 215 ps by controlling the gate voltage. The gate tunable dark trions ushers in new opportunities for excitonic optoelectronics and valleytronics.

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Emerging photoluminescence from the dark-exciton phonon replica in monolayer WSe2

Cited by 133 publications

References 55 publications

Valley phonons and exciton complexes in a monolayer semiconductor

Valley phonons and exciton complexes in a monolayer semiconductor

Momentum-Dark Intervalley Exciton in Monolayer Tungsten Diselenide Brightened via Chiral Phonon

Direct Observation of Gate-Tunable Dark Trions in Monolayer WSe₂

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Emerging photoluminescence from the dark-exciton phonon replica in monolayer WSe2

Cited by 133 publications

References 55 publications

Valley phonons and exciton complexes in a monolayer semiconductor

Valley phonons and exciton complexes in a monolayer semiconductor

Momentum-Dark Intervalley Exciton in Monolayer Tungsten Diselenide Brightened via Chiral Phonon

Direct Observation of Gate-Tunable Dark Trions in Monolayer WSe2

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Direct Observation of Gate-Tunable Dark Trions in Monolayer WSe₂