Anomalous temperature-dependent spin-valley polarization in monolayer WS${}_2$

Abstract

Single layers of transition metal dichalcogenides (TMDs) are direct gap semiconductors with nondegenerate valley indices. An intriguing possibility for these materials is the use of their valley index as an alternate state variable. Several limitations to such a utility include strong, phonon-enabled intervalley scattering, as well as multiparticle interactions leading to multiple emission channels. We prepare single-layer WS${}_2$ such that the photoluminescence is from either the neutral or charged exciton (trion). After excitation with circularly polarized light, the neutral exciton emission has zero polarization, however, the trion emission has a large polarization (28%) at room temperature. The trion emission also has a unique, non-monotonic temperature dependence that we show is a consequence of the multiparticle nature of the trion. This temperature dependence enables us to determine that coulomb assisted intervalley scattering, electron-hole radiative recombination, and a 3-particle Auger process are the dominant mechanisms at work in this system. Because this dependence involves trion systems, one can use gate voltages to modulate the polarization (or intensity) emitted from TMD structures.

26 pages, 4 figures, includes supplementary information

References in corpus (14)

• Valley polarization in MoS2 monolayers by optical pumping
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• Valley filter and valley valve in graphene
• Tightly bound excitons in monolayer WSe2
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• Robust optical emission polarization in MoS2 monolayers through selective valley excitation
• Valley susceptibility of an interacting two-dimensional electron system
• Measurement of high exciton binding energy in the monolayer transition-metal dichalcogenides WS2 and WSe2
• Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
• Temperature Dependent Valley Relaxation Dynamics in Single Layer WS2 Measured Using Ultrafast Spectroscopy
• Optical control of charged exciton states in tungsten disulfide

Cited by in corpus (20)

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• Direct exciton emission from atomically thin transition metal dichalcogenide heterostructures near the lifetime limit
• The Effect of Preparation Conditions on Raman and Photoluminescence of Monolayer WS2
• Optical valley Hall effect for highly valley-coherent exciton-polaritons in an atomically thin semiconductor
• Tuning the Fröhlich exciton-phonon scattering in monolayer MoS2
• Singlet and triplet trions in WS${}_2$ monolayer encapsulated in hexagonal boron nitride
• Understanding Variations in Circularly Polarized Photoluminescence in Monolayer Transition Metal Dichalcogenides
• Imaging Spin Dynamics in Monolayer WS2 by Time-Resolved Kerr Rotation Microscopy
• Valley polarized relaxation and upconversion luminescence from Tamm-Plasmon Trion-Polaritons with a MoSe2 monolayer
• Observation of macroscopic valley-polarized monolayer exciton-polaritons at room temperature
• Prominent room temperature valley polarization in WS2/graphene heterostructures grown by chemical vapor deposition
• Radiative lifetime of localized excitons in transition metal dichalcogenides
• Exciton-to-trion conversion as a control mechanism for valley polarization in room-temperature monolayer WS${}_{\text{2}}$
• Effects of CVD Growth Parameters on Global and Local Optical Properties of MoS${}_2$ Monolayers
• Phonon-assisted exciton and trion conversion efficiency in transition metal Dichalcogenides
• Magnetic field induced splitting and polarization of monolayer-based valley exciton-polaritons
• Electron spin dynamics of two-dimensional layered materials
• Biaxial strain tuning of exciton energy and polarization in monolayer WS2
• Manipulating single photon emitter radiative lifetime in transition-metal dichalcogenides through Forster resonance energy transfer to graphene
• Laser-patterned submicron Bi2Se3-WS2 pixels with tunable circular polarization at room temperature