Double resonant Raman scattering and valley coherence generation in monolayer WSe2

Abstract

The electronic states at the direct band gap of monolayer WSe2 at the $K^{+}$ and $K^{-}$ valleys are related by time reversal and may be viewed as pseudo-spins. The corresponding optical interband transitions are governed by robust excitons. In double resonant Raman spectroscopy, we uncover that the 2s exciton state energy differs from the 1s state energy by exactly the energy of the combination of several prominent phonons. Superimposed on the exciton photoluminescence (PL) we observe the double resonant Raman signal. This spectrally narrow peak shifts with the excitation laser energy as incoming photons match the 2s and outgoing photons the 1s exciton transition. The multi-phonon resonance has important consequences: Following linearly polarized excitation of the 2s exciton a superposition of valley states is generated which can relax fast via phonon emission and with minimal loss of coherence from the 2s to 1s state. This explains the high degree of valley coherence measured for the 1s exciton PL.

5 pages, 3 figures, supplement

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Cited by in corpus (31)

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• Room temperature Tamm-Plasmon Exciton-Polaritons with a WSe2 monolayer
• Control of Exciton Valley Coherence in Transition Metal Dichalcogenide Monolayers
• Microsecond Valley Lifetime of Defect-Bound Excitons in Monolayer WSe${}_2$
• Enabling valley selective exciton scattering in monolayer WSe${}_2$ through upconversion
• Exciton-phonon coupling in MoSe2 monolayers
• Long-Lived Valley Polarization of Intra-Valley Trions in Monolayer WSe2
• Optical spectroscopy of excited exciton states in MoS2 monolayers in van der Waals heterostructures
• Unusual Exciton-Phonon Interactions at van der Waals Engineered Interfaces
• Valley coherent exciton-polaritons in a monolayer semiconductor
• Excitonic properties of semiconducting monolayer and bilayer MoTe2
• Strongly coupled coherent phonons in single-layer MoS${}_2$
• Exciton states in monolayer MoSe2 and MoTe2 probed by upconversion spectroscopy
• Phonon-assisted oscillatory exciton dynamics in monolayer MoSe2
• Observation of forbidden phonons and dark excitons by resonance Raman scattering in few-layer WS${}_2$
• Trion Valley Coherence in Monolayer Semiconductors
• Superior valley polarization and coherence of 2s excitons in monolayer WSe2
• Virtual trions in the photoluminescence of monolayer transition-metal dichalcogenides
• Ab Initio Approach to Second-order Resonant Raman Scattering Including Exciton-Phonon Interaction
• Novel approach to Raman spectra of nanoparticles
• Valley Degree of Freedom in Two-Dimensional van der Waals Materials
• Phonon-assisted exciton and trion conversion efficiency in transition metal Dichalcogenides
• Valley polarization of exciton-polaritons in monolayer WSe2 in a tunable microcavity
• Disorder Dependent Valley Properties in Monolayer WSe2
• Interlayer exciton-polaron in atomically thin semiconductors
• Phonon-induced exciton weak localization in two-dimensional semiconductors
• Flexural deformations and collapse of bilayer two-dimensional crystals by interlayer exciton
• Magnetically tunable exciton valley coherence in monolayer WS${}_2$ mediated by the electron-hole exchange and exciton-phonon interactions
• Spin transport in n-type single-layer transition metal dichalcogenides
• Laser-field detuning assisted optimization of exciton valley dynamics in monolayer WSe${}_2$: Geometric quantum speed limit
• Non-Hermitian theory of valley excitons in two-dimensional semiconductors