Magnetic and electric control of spin- and valley-polarized transport across tunnel junctions on monolayer WSe2

Abstract

The recent experimental realization of high-quality ${\mathrm{WSe}}_{2}$ leads to the possibility of an efficient manipulation of its spin and valley degrees of freedom. Its electronic properties comprise a huge spin-orbit coupling, a direct band gap, and a strong anisotropic lifting of the degeneracy of the valley degree of freedom in a magnetic field. We evaluate its band structure and study ballistic electron transport through single and double junctions (or barriers) on monolayer ${\mathrm{WSe}}_{2}$ in the presence of spin ${M}_{s}$ and valley ${M}_{v}$ Zeeman fields and of an electric potential $U$. The conductance versus the field ${M}_{s}$ or ${M}_{v}$ decreases in a fluctuating manner. For a single junction, the spin ${P}_{s}$ and valley ${P}_{v}$ polarizations rise with $M={M}_{v}=2{M}_{s}$, reach a value of more than $55%$, and become perfect above $U\ensuremath{\approx}45$ meV while for a double junction this change can occur for $U\ensuremath{\ge}50$ meV and $M\ensuremath{\ge}5$ meV. In certain regions of the $(M,U)$ plane ${P}_{v}$ becomes perfect. The conductance ${g}_{c}$, its spin-up and spin-down components, and both polarizations oscillate with the barrier width $d$. The ability to isolate various carrier degrees of freedom in ${\mathrm{WSe}}_{2}$ may render it a promising candidate for new spintronic and valleytronic devices.