Ultrafast Optical Control of Exciton Diffusion in WSe₂/Graphene Heterostructures Revealed by Heterodyne Transient...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) semiconductors like tungsten diselenide (WSe₂) exhibit unique electronic properties.
• Understanding exciton dynamics is crucial for developing advanced optoelectronic devices.
• Heterostructures combining 2D materials with graphene offer tunable functionalities.

Purpose of the Study:

• To investigate exciton diffusion enhancement in WSe₂/graphene heterostructures.
• To explore the optical tunability of diffusion dynamics.
• To elucidate the mechanisms behind enhanced exciton transport.

Main Methods:

• Heterodyne transient grating spectroscopy was employed.
• Exciton diffusion in WSe₂ monolayer on graphene was measured.
• Photoexcited carrier density in graphene was varied to tune dynamics.

Main Results:

• A significant enhancement of exciton diffusion was observed in WSe₂/graphene compared to isolated WSe₂.
• The effective diffusion constant increased from 2.1 cm² s^-1 to 40.3 cm² s^-1.
• Diffusion dynamics were optically tunable on picosecond timescales via graphene carrier density.

Conclusions:

• Transient screening of WSe₂ defects by photoexcited graphene carriers enhances exciton diffusion.
• Interlayer charge transfer and screening effects are dynamically modulated by excitation fluence.
• Findings provide insights into ultrafast optoelectronics utilizing 2D semiconductor heterostructures.