Manipulation of the Rashba spin-orbit coupling of a distorted 1T-phase Janus WSSe monolayer: Dominant role of charge transfer and orbital components

Abstract

Janus monolayer materials, as the thinnest materials that may possess strong Rashba spin-orbit coupling, are helpful for the miniaturization of the charge-spin conversion devices. Using first-principles calculations, we investigated the structural stability and Rashba spin-orbit coupling of distorted $1T\text{-phase}$ Janus monolayer WSSe. Although the W atoms rotating around the Se atom are dynamically unstable in the stress-free state, the imaginary frequency disappears by applying a small compressive strain. From the perspectives of macroscopic charge transfer and microscopic atomic orbital compositions, the mechanism of the Rashba spin-orbit coupling strength of the distorted $1T\text{-phase}$ Janus monolayer WSSe was analyzed. The coupling strength can be greatly manipulated when \ensuremath{-}5 to 5% biaxial strain is applied. The charge transfer caused by the larger lattice constant and the rotation of the W atoms reduce the gradient of the potential so that the greater the electric polarization, the weaker the spin-orbit coupling. The coupling strength of different electronic states is determined by the proportion of the out-of-plane atomic orbitals, where ${d}_{\mathrm{x}z}$ and ${d}_{yz}$ orbits play the dominant role. These results contribute to the design of materials with greater Rashba spin-orbit coupling and the understanding of its mechanism.