Enhanced Valley Polarization of Bilayer MoSe₂ with Variable Stacking Order and Interlayer Coupling.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional transitional metal dichalcogenides (TMDs) offer tunable spin-valley-layer coupling.
• Valleytronics applications require precise control over these couplings, particularly through layer number and stacking order.

Purpose of the Study:

• To investigate the impact of different stacking orders (2H and 3R) on valley polarization in molybdenum diselenide (MoSe2) nanoflakes.
• To explore the potential of controlled stacking for enhancing valley polarization in TMDs.

Main Methods:

• Fabrication of six-point star-like MoSe2 nanoflakes with varying layer numbers and stacking orders (monolayer to bilayer, 2H and 3R).
• Comparative investigation of valley polarizations using circular polarized photoluminescent spectroscopy.
• Ab initio calculations to analyze energy band structures and spin-dependent phenomena.

Main Results:

• Valley polarization was measured at approximately 12.5% in monolayer and 10% in 2H bilayer MoSe2.
• A significant enhancement to about 40% valley polarization was observed in 3R bilayer MoSe2.
• Ab initio calculations confirmed multiband spin splitting and spin-dependent layer polarization in 3R MoSe2.

Conclusions:

• Controllable stacking orders, specifically the 3R configuration, are crucial for significantly boosting valley polarization in MoSe2.
• This work demonstrates a viable strategy for tuning valley indices in TMDs, paving the way for advanced valleytronics devices.