Anisotropic Rashba effect in two-dimensional non-Janus transition-metal dichalcogenide, MSSe (M=Mo,W) alloys

The breaking of the out of plane mirror symmetry in the Janus transition-metal dichalcogenides (TMDs) has made them appealing candidates for optoelectronic, spintronic, valleytronic, and photocatalytic applications. In this study, we compare the structural and electronic properties of the Janus structure with the more stable TMD alloys of the form $M\mathrm{SSe} (M=\mathrm{Mo},\mathrm{W})$. The charge distribution analysis and two-dimensional electron localization function analysis indicate that the geometry of the system plays a vital role in determining the magnitude of the metal to ligand charge transfer, which in turn dictates the stability of the alloys. The arrangement of the chalcogen atoms in the more stable alloy allows for a better charge distribution, resulting in superior stability. Band structure calculations reveal that both structures are semiconducting with identical direct band gaps and exhibit Rashba splitting near the \ensuremath{\Gamma} point in the presence of the spin-orbit coupling (SOC) effects. While in the Janus structures, the broken mirror symmetry gives rise to an out of plane uniform electric field, the reduced symmetry of the more stable alloy structure produces an anisotropic arrangement of the perpendicular dipole moments. The nonuniformity of the electric dipole moments is reflected in the Rashba effect, which has an anisotropic nature, unlike the isotropic Rashba splitting observed in the Janus structures.