Dark excitons and the elusive valley polarization in transition metal dichalcogenides

Abstract

A rate equation model for the dark and bright excitons kinetics is proposed which explains the wide variation in the observed degree of circular polarization of the PL emission in different TMDs monolayers. Our work suggests that the dark exciton states play an important, and previously unsuspected role in determining the degree of polarization of the PL emission. A dark exciton ground state provides a robust reservoir for valley polarization, which tries to maintain a Boltzmann distribution of the bright exciton states in the same valley via the intra valley bright dark exciton scattering mechanism. The dependence of the degree of circular polarization on the detuning energy of the excitation in MoSe${}_2$ suggests that the electron-hole exchange interaction dominates over two LA phonon emission mechanism for inter valley scattering in TMDs.

text without changes, the misspelling of one of the names corrected

References in corpus (13)

• Valley polarization in MoS2 monolayers by optical pumping
• Tightly bound excitons in monolayer WSe2
• Valley Dependent Optoelectronics from Inversion Symmetry Breaking
• Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
• Magnetic Control of Valley Pseudospin in Monolayer WSe2
• Ultrafast Dynamics of Defect-Assisted Electron-Hole Recombination in Monolayer MoS2
• Light Generation and Harvesting in a Van der Waals Heterostructure
• Exciton Valley Dynamics probed by Kerr Rotation in WSe2 Monolayers
• Phonon Softening and Direct to Indirect Bandgap Crossover in Strained Single Layer MoSe2
• Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
• Exciton and trion dynamics in atomically thin MoSe2 and WSe2: effect of localization
• Temperature Dependent Valley Relaxation Dynamics in Single Layer WS2 Measured Using Ultrafast Spectroscopy
• Population pulsation resonances of excitons in monolayer MoSe2 with sub 1 μeV linewidth

Cited by in corpus (6)

• Probing the inter-layer exciton physics in a MoS${}_2$/MoSe${}_2$/MoS${}_2$ van der Waals heterostructure
• Observation of exciton-exciton interaction mediated valley depolarization in monolayer MoSe${}_2$
• 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
• Long-lived spin polarization in n-doped MoSe${}_2$ monolayers
• Optical Measurement of Pseudo-Spin Texture of the Exciton Fine-Structure in Monolayer WSe2 within the Light Cone