Enabling valley selective exciton scattering in monolayer WSe₂ through upconversion

Area of Science:

• Condensed matter physics
• Materials science
• Quantum optics

Background:

• Excitons, as composite bosons, drive phenomena like condensation and light amplification in semiconductors.
• Transition metal dichalcogenides (TMDs), like WSe2 monolayers, exhibit strong Coulomb interactions and valley degrees of freedom, offering novel excitonic control.
• The exploration of exciton scattering processes, particularly their bosonic character, remains underdeveloped in 2D materials.

Purpose of the Study:

• Investigate exciton scattering dynamics in WSe2 monolayers.
• Explore the role of the valley degree of freedom in exciton-exciton interactions.
• Characterize the polarization properties of emitted light resulting from exciton scattering.

Main Methods:

• Utilized a selective upconversion technique to generate B-excitons efficiently.
• Resonantly excited lower-energy A-excitons in WSe2 monolayers.
• Analyzed power-dependent emission spectra and polarization characteristics.

Main Results:

• Demonstrated that scattering between A-excitons and B-excitons predominantly occurs within the same valley.
• Observed power-dependent, negative polarization in the hot B-exciton emission.
• Successfully generated B-excitons via upconversion in the presence of excited A-excitons and observed the 2s state of A-excitons.

Conclusions:

• Exciton-exciton scattering in WSe2 monolayers is valley-selective, influencing emission polarization.
• The findings provide insights into controlling excitonic effects in 2D materials through valley interactions.
• Selective upconversion is a viable technique for studying exciton dynamics in WSe2.