Momentum-Resolved Exciton Coupling and Valley Polarization Dynamics in Monolayer WS${}_2$

Abstract

Coupling between exciton states across the Brillouin zone in monolayer transition metal dichalcogenides can lead to ultrafast valley depolarization. Using time- and angle-resolved photoemission, we present momentum- and energy-resolved measurements of exciton coupling in monolayer WS${}_2$. By comparing full 4D ($k_x,k_y,E,t$) data sets after both linearly and circularly polarized excitation, we are able to disentangle intervalley and intravalley exciton coupling dynamics. Recording in the exciton binding energy basis instead of excitation energy, we observe strong mixing between the B${}_{1s}$ exciton and A${}_{n>1}$ states. The photoelectron energy and momentum distributions observed from excitons populated via intervalley coupling (e.g. K${}^{-}$ $\to$ K${}^{+}$) indicate that the dominant valley depolarization mechanism conserves the exciton binding energy and center-of-mass momentum, consistent with intervalley Coulomb exchange. On longer timescales, exciton relaxation is accompanied by contraction of the momentum space distribution.

arXiv comment16 pages: 8 pages main text with 5 figures, 8 pages SI with 6 figures

References in corpus (58)

• Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides
• Control of valley polarization in monolayer MoS2 by optical helicity
• Valley polarization in MoS2 monolayers by optical pumping
• Emerging Device Applications for Semiconducting Two-Dimensional Transition Metal Dichalcogenides
• MoS_2 as an ideal material for valleytronics: valley-selective circular dichroism and valley Hall effect
• Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer WS2
• Valley contrasting physics in graphene: magnetic moment and topological transport
• Excitons in atomically thin transition metal dichalcogenides
• Optical Spectrum of MoS${}_2$: Many-body Effects and Diversity of Exciton States
• Optical Generation of Excitonic Valley Coherence in Monolayer WSe2
• Measurement of the optical dielectric function of transition metal dichalcogenide monolayers: MoS2, MoSe2, WS2 and WSe2
• Valley Dependent Optoelectronics from Inversion Symmetry Breaking
• k.p theory for two-dimensional transition metal dichalcogenide semiconductors
• Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides
• Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors
• Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides
• Robust optical emission polarization in MoS2 monolayers through selective valley excitation
• Valley dynamics probed through charged and neutral exciton emission in monolayer WSe2
• Carrier and polarization dynamics in monolayer MoS2
• In-plane Propagation of Light in Transition Metal Dichalcogenide Monolayers: Optical Selection Rules
• Bright excitons in monolayer transition metal dichalcogenides: from Dirac cones to Dirac saddle points
• Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS${}_2$ and MoS${}_2$ to 65 Tesla
• Valley depolarization due to inter- and intra-valley electron-hole exchange interactions in monolayer MoS${}_2$
• Direct Measurement of Exciton Valley Coherence in Monolayer WSe${}_2$
• Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides
• Exciton Valley Dynamics probed by Kerr Rotation in WSe2 Monolayers
• Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
• Anomalously Robust Valley Polarization and Valley Coherence in Bilayer WS2
• Nonanalyticity, Valley Quantum Phases, and Light-like Exciton Dispersion in Monolayer TMDs: Theory and First-Principles Calculations
• Directly visualizing the momentum forbidden dark excitons and their dynamics in atomically thin semiconductors
• Optical properties of atomically thin transition metal dichalcogenides: Observations and puzzles
• Exciton Dynamics in Monolayer Transition Metal Dichalcogenides
• Excitons versus electron-hole plasma in monolayer transition metal dichalcogenide semiconductors
• Valley Phonons and Exciton Complexes in a Monolayer Semiconductor
• Observation of Ultrafast Free Carrier Dynamics in Single Layer MoS${}_2$
• Formation of moiré interlayer excitons in space and time
• Gate controlled spin-valley locking of resident carriers in WSe2 monolayers
• Spin and valley dynamics of excitons in transition metal dichalcogenides monolayers
• Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer MoS2
• Temperature Dependent Valley Relaxation Dynamics in Single Layer WS2 Measured Using Ultrafast Spectroscopy
• Momentum-resolved observation of exciton formation dynamics in monolayer WS${}_2$
• Ultrafast extreme ultraviolet photoemission without space charge
• Dark excitons and the elusive valley polarization in transition metal dichalcogenides
• Photoemission signature of excitons
• Ultrafast dynamics in monolayer TMDCs: the interplay of dark excitons, phonons and intervalley Coulomb exchange
• Theory of exciton dynamics in time-resolved ARPES: intra- and intervalley scattering in two-dimensional semiconductors
• Intrinsic exciton states mixing and non-linear optical properties in transition metal dichalcogenide monolayers
• Imaging Spin Dynamics in Monolayer WS2 by Time-Resolved Kerr Rotation Microscopy
• Observation of exciton-exciton interaction mediated valley depolarization in monolayer MoSe${}_2$
• High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools
• Spin and Valley Control of Free Carriers in Single-Layer WS${}_2$
• Superior valley polarization and coherence of 2s excitons in monolayer WSe2
• Larger than 80% Valley Polarization of Free Carriers in Singly-Oriented Single Layer WS${}_2$ on Au(111)
• Quenching of Intervalley Exchange Coupling in the Presence of Momentum-Dark States in TMDCs
• Valley-Polarized Exciton Dynamics in Exfoliated Monolayer WSe${}_2$
• Coherent exciton-exciton interactions and exciton dynamics in a MoSe\textsubscript{2}/WSe\textsubscript{2} heterostructure
• Control of the exciton valley dynamics in van der Waals heterostructures
• Long-lived spin polarization in n-doped MoSe${}_2$ monolayers

Cited by in corpus (14)

• Time- and Angle-Resolved Photoemission Studies of Quantum Materials
• Roadmap for Photonics with 2D Materials
• Ultrafast dynamics of bright and dark excitons in monolayer WSe${}_2$ and heterobilayer WSe${}_2$/MoS${}_2$
• Advancing time- and angle-resolved photoemission spectroscopy: The role of ultrafast laser development
• Vibrational dichroism of chiral valley phonons
• Probing correlations in the exciton landscape of a moiré heterostructure
• Multiorbital exciton formation in an organic semiconductor
• Ultrafast nano-imaging of dark excitons
• Probing excitons with time-resolved momentum microscopy
• Multi-Mode Lens for Momentum Microscopy and XPEEM: Theory
• Review: Advanced characterization of the spatial variation of moiré heterostructures and moiré excitons
• Hybrid Frenkel-Wannier excitons facilitate ultrafast energy transfer at a 2D-organic interface
• Momentum-space Observation of Optically Excited Non-Thermal Electrons in Graphene with Persistent Pseudospin Polarization
• Asymmetric Electrostatic Dodecapole: Compact Bandpass Filter with Low Aberrations for Momentum Microscopy