Observation of exciton-exciton interaction mediated valley depolarization in monolayer MoSe${}_2$

Abstract

The valley pseudospin in monolayer transition metal dichalcogenides (TMDs) has been proposed as a new way to manipulate information in various optoelectronic devices. This relies on a large valley polarization that remains stable over long timescales (hundreds of ns). However, time resolved measurements report valley lifetimes of only a few ps. This has been attributed to mechanisms such as phonon-mediated inter-valley scattering and a precession of the valley psedospin through electron-hole exchange. Here we use transient spin grating to directly measure the valley depolarization lifetime in monolayer MoSe${}_2$. We find a fast valley decay rate that scales linearly with the excitation density at different temperatures. This establishes the presence of strong exciton-exciton Coulomb exchange interactions enhancing the valley depolarization. Our work highlights the microscopic processes inhibiting the efficient use of the exciton valley pseudospin in monolayer TMDs.

References in corpus (8)

• Valley polarization in MoS2 monolayers by optical pumping
• Ultrafast Dynamics of Defect-Assisted Electron-Hole Recombination in Monolayer MoS2
• Emergence of the persistent spin helix in semiconductor quantum wells
• 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
• Dark excitons and the elusive valley polarization in transition metal dichalcogenides
• Spin relaxation in $n$-type GaAs quantum wells with transient spin grating

Cited by in corpus (5)

• Exciton-Scattering-Induced Dephasing in Two-Dimensional Semiconductors
• Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides
• Transient Grating Spectroscopy of Photocarrier Dynamics in Semiconducting Polymer Thin Films
• Excitonic Transport and Intervalley Scattering in Exfoliated MoSe2 Monolayer Revealed by Four-Wave-Mixing Transient Grating Spectroscopy
• Enhancement of valley polarization at high photoexcited densities in MoS2 monolayers