Two-dimensional spin-valley locking spin valve

Valleytronics is an emerging field of research which employs energy valleys in the band structure of two-dimensional (2D) electronic materials to encode information. A special interest has been triggered by the associated spin-valley coupling which reveals rich fundamental physics and enables new functionalities. Here, we propose exploiting the spin-valley locking in 2D materials with a large spin-orbit coupling and electric-field reversible valley spin polarization, such as germanene, stanene, a $1{T}^{\ensuremath{'}}$ transition metal dichalcogenide (TMDC) monolayer, and a $2H$-TMDC bilayer, to realize a valley spin valve (VSV). The valley spin polarization in these materials can be switched by an external electric field, which enables functionalities of a valley spin polarizer or a valley spin analyzer. When placed in series, they constitute the proposed VSV---a device whose conductance state is ON or OFF depending on the relative valley spin polarization of the polarizer and the analyzer. Using quantum-transport calculations based on an adequate tight-binding model, we predict a giant VSV ratio of nearly 100% for both germanene- and stanene-based VSV devices. Our results demonstrate the implication of the spin-valley coupling in 2D materials for the novel device concept promising for valleytronics.