Bias-driven spontaneous spin-valley polarization in monolayer transition-metal dichalcogenides

A physical mechanism that may enable electrical control of carrier spin-valley polarization is theoretically examined in a monolayer transition-metal dichalcogenide (TMD) structure. The idea is based on the interplay between the strongly spin-orbit coupled nature of the TMD band structure and the exchange interaction with a proximate magnet that can spontaneously lift the valley degeneracy when the carrier density exceeds a certain threshold. The analysis based on the free energy of the system clearly illustrates the desired spin-valley polarization in the TMD layer as well as the accompanying rotational phase transition in the magnetization. Numerical estimates utilizing the WS₂ parameters as an example indicate a sharp transition in the spin-valley polarization over tens of percent at room temperature with only a modest change in the electrochemical potential of a few meV via electrostatic bias. Detection of the predicted phenomenon is expected to be straightforward through the corresponding modification in the TMD channel conductance.