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Up- and Down-Conversion between Intra- and Intervalley Excitons in Waveguide Coupled Monolayer WSe2
Yueh-Chun Wu1, Sarath Samudrala2, Andrew McClung2
1Department of Physics, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States.
ACS Nano
|July 21, 2020
Summary
Researchers developed a waveguide device to study dark excitons in tungsten diselenide (WSe2) monolayers. This method efficiently populates spin-dark excitons, revealing complex couplings and common spin-flip processes in 2D semiconductors.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanotechnology
Background:
- Monolayer transition metal dichalcogenides (TMDs) possess two spin-split valleys, enabling diverse exciton species.
- Bright excitons (spin-0 intravalley) are easily observed, but spin-dark (spin-1 intravalley) and momentum-dark (spin-0 intervalley) excitons are challenging to access.
Purpose of the Study:
- To develop a method for probing and populating less accessible exciton species in monolayer TMDs.
- To investigate the coupling network and scattering processes between different exciton types.
Main Methods:
- Fabrication of a waveguide-coupled monolayer tungsten diselenide (WSe2) device.
- Utilizing TM coupling to atomic layer out-of-plane dipole moments for exciton manipulation.
- Resonant population and efficient collection of spin-dark excitons.
Main Results:
- Efficient collection and resonant population of spin-1 dark excitons in WSe2.
- Observation of multiple upconversion processes, indicating an intricate coupling network.
- Demonstration that intervalley scattering and spin-flip are common in monolayer TMDs.
Conclusions:
- Planar photonic devices can harness versatile exciton species in TMD semiconductors.
- The developed waveguide approach is promising for creating devices with long valley lifetimes.
- This study deepens the understanding of exciton physics in WSe2 and related 2D materials.
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