Visualizing Nanoscale Valley Polarization in Transition Metal Dichalcogenides Using Tip-Enhanced Circularly Polarized...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Valley polarization in transition metal dichalcogenides (TMDs) is crucial for valleytronic devices.
• Conventional optical techniques lack the spatial resolution to map nanoscale valley polarization.
• Local inhomogeneities significantly impact TMD valleytronic device performance.

Purpose of the Study:

• To introduce and demonstrate tip-enhanced circularly polarized photoluminescence (TECPPL) imaging for nanoscale valley polarization mapping.
• To investigate the spatial distribution of valley polarization in a monolayer MoS2/WS2 heterojunction.
• To achieve high spatial resolution for visualizing variations in exciton emission and valley polarization.

Main Methods:

• Tip-enhanced circularly polarized photoluminescence (TECPPL) imaging.
• Near-field (NF) and far-field (FF) photoluminescence (PL) measurements.
• Investigation of a monolayer (1L) MoS2/WS2 heterojunction (HJ).

Main Results:

• TECPPL imaging enables simultaneous mapping of exciton emission intensity and valley polarization.
• Pronounced NF photoluminescence enhancement was observed under different polarization configurations.
• Achieved a NF circular polarization degree (Pc) of 0.67, a 4-fold increase over FF measurements.
• Demonstrated a spatial resolution of approximately 20 nm for visualizing PL intensity and Pc variations.

Conclusions:

• TECPPL is a powerful nanospectroscopic tool for studying valleytronics.
• The study provides new insights into the spatially resolved valleytronic behavior of TMD heterostructures.
• High spatial resolution mapping of valley polarization is now achievable, advancing TMD device research.