Electrically controlled dc and ac transport in bilayer WSe2

We investigate quantum transport in a bilayer WSe2 in the presence of an external potential V and interlayer coupling. The dc and ac conductivities are evaluated in the framework of linear response theory. As functions of the Fermi energy, the dc ones exhibit a nonmonotonic behavior with a flat region in the band gap. A deep local minimum is visible in spin-Hall conductivity near the top of the valence band as a consequence of a large valence band splitting. On the other hand, the ac spin- and valley-Hall conductivities, as functions of the frequency, show two opposite peaks near the top of the valence band. The spin-Hall conductivity exhibits a minimum value at V = 0 whereas the valley-Hall conductivity decreases monotonically upon varying V from negative to positive values. Furthermore, we evaluate the power absorption spectrum and assess its dependence on the spin and valley degrees of freedom. The results are pertinent to the development of electrically controlled spintronic and valleytronic devices based on bilayer WSe2 and other group VI semiconductors.