Enhanced spin-orbit coupling in single layer CVD WSe2/graphene heterostructures

Spin-orbit coupling (SOC) in graphene can be strongly enhanced via proximity effect when graphene is in contact with transition metal dichalcogenides (TMDs) [1]. However, bulk TMDs are hard to be exfoliated to single or few layers while maintaining a practically large size. An alternative approach by using chemical vapor deposition (CVD) grown WSe$_{\mathrm{2}}$ allows us to overcome this obstacle. We have succeeded in picking up a single layer CVD WSe$_{\mathrm{2}}$ flake with hBN and transferring it onto an exfoliated graphene flake. Due to the lower carrier density per unit area of the CVD WSe$_{\mathrm{2}}$, we are able to tune the Fermi level in graphene over a wide range, and observe a clear weak antilocalization at various carrier densities, indicating a strong enhancement of the SOC strength in graphene due to the proximity interaction of the WSe$_{\mathrm{2}}$. Meanwhile, the universal conductance fluctuation is also suppressed owing to the large size of the WSe$_{\mathrm{2}}$. We extract the spin relaxation time which is roughly one fourth that of previously studied WS$_{\mathrm{2}}$/graphene heterostructures [1] and thus a 100{\%} increase in the SOC strength. [1] B. Y. et al., 2D Mater. 3, 031012 (2016).