First-principles study of the role of Kitaev interaction in monolayer 1T-CoI₂

Kitaev interactions, which are bond-related anisotropic interactions induced by spin-orbit coupling(SOC), may produce quantum spin liquid states in 2D magnetic hexagonal lattices such as RuCl₃. Generally the strong SOC in these materials come from heavy metal elements such as Ru in RuCl₃. In recent years, some related studies have shown the presence of Kitaev effects in some 2D monolayers of ortho-octahedral structures containing heavy ligand elements, such as CrGeTe₃, CrSiTe₃, and so on. However, there are relatively few reports on the Kitaev interactions in 2D monolayer 1T structures. In this paper, we have calculated and analysed the atomic and electronic structures of 1T-CoI₂ and the Kitaev interactions contained therein by means of the first-principles calculation program VASP. The structure of 1T-CoI₂ is a triangular lattice with an emphasis on the coordinating element I. The energy dispersion relation E_S( q )=E_N+S( q )-E_N( q ) for the contained Kitaev action was isolated by calculating the energy dispersion relation E_N( q ) for the spin-spiral of a monolayer CoI₂ without SOC and the energy dispersion relation E_N+S( q ) considering SOC using the generalised Bloch condition combined with the spin-spiral method. The parameters of the Heisenberg exchange interaction induced by the SOC were obtained by fitting the dispersion law of the E_S( q ) to the Kitaev exchange interaction with the parameters of the Kitaev exchange interaction. The fitted curves obtained with the fitted parameters are in good agreement with the calculated values, indicating the accuracy of our calculations. Calculated fits show that the monolayer CoI₂ is dominated by Heisenberg action, with the third nearest neighbour having the largest absolute value of J at -1.81 meV. In addition to this, there are strong Kitaev interactions in monolayer CoI₂, where Γ₁ reaches 1.09 meV. We predict that Kitaev interactions are universally applicable in transition metal triangular lattices with 1T structure. It is shown that CoI₂ can be used as an alternative material for Kitaev and lays a theoretical foundation for exploring Kitaev interactions in other 2D magnetic materials.