Chiral orbital/spin textures and Edelstein effects in monolayer Janus TMDs

We investigate the orbital and spin Edelstein effect(OEE and SEE) in two-dimensional Janus transition metal dichalcogenides (TMDs) of the form MXX${}^{\mathrm{\prime }}$ $(M=Mo,W,Nb;X\mathrm{/}{X}^{\mathrm{\prime }}=S,Se,Te)$ with the aid of density functional theory calculations and tight-binding model Hamiltonian studies. The chalcogen layers $X$ and $X^{\mathrm{\prime }}$, break the mirror symmetry to introduce an internal electric field $E_{int}$ normal to the plane, which is responsible for OEE and SEE. Our results show that in a non-Janus framework, the wavefunctions at the valence and conduction bands are dominated with the $\mathrm{\mid }{x}^2-y^2>$, $\mathrm{\mid }xy>$, and $\mathrm{\mid }{z}^2>$ orbitals. Due to the $E_{int}$ of the Janus system, these orbitals are now intermixed with the $\mathrm{\mid }xz>$ and $\mathrm{\mid }yz>$ orbitals to produce a robust orbital texture around the valleys $\mathrm{\Gamma },K$ and $K^{\mathrm{\prime }}$. The spin orbit coupling, in addition to the formation of a spin texture, introduces a chirality reversal to the orbital texture. An applied in plane electric field creates both OEE and SEE with the former being one order higher in magnitude. This makes the Janus materials promising for spin-orbitronics. Our work paves the way for further experimental exploration for orbital and spin orbital torque in Janus TMDs.