posted on 2021-06-18, 18:00authored byXingli Zhang, Jun Zhou, Shi-Qi Li, Yuanye Wang, Shiping Zhang, Yalin Liu, Junfeng Gao, Jijun Zhao, Weipeng Wang, Richeng Yu, Weifeng Zhang, Nan Liu, Jiacai Nie, Lin He, Ruifen Dou
In
two-dimensional transitional metal dichalcogenides, tuning the
spin-valley-layer coupling via changing layer numbers and stacking
orders remains desirable for their application in valleytronics. Herein,
six-point star-like MoSe2 nanoflakes simultaneously containing
different atom registration regions from monolayer to bilayer with
2H and 3R stacking order were fabricated, and the valley polarizations
were comparably investigated by circular polarized photoluminescent
spectroscopy. The degree of valley polarization was detected to be
about 12.5% in the monolayer and 10% in the 2H bilayer, but greatly
upgraded to about 40% in the 3R bilayer MoSe2. This enhancement
was attributed to the multiband spin splitting and generation of spin-dependent
layer polarization for the 3R MoSe2 bilayer, which is well
evidenced by our ab initio calculations of the energy
band structures. Our results demonstrate that preparing TMD crystals
with controllable stacking orders and interlayer coupling is a promising
route to tune the valley index in TMDs for developing valleytronics
technology.