First-principles study of 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 two-dimensional (2D) magnetic hexagonal lattices such as RuCl3. Generally, the strong SOCs 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 orthooctahedral structures containing heavy ligand elements, such as CrGeTe3 and CrSiTe3. However, there are relatively few reports on the Kitaev interactions in 2D monolayer 1T structures. In this paper, we calculate and analyse the atomic and electronic structures of 1T-CoI2 and the Kitaev interactions contained therein by 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) = EN+S (q) - E-N (q) for the contained Kitaev action is isolated by calculating the energy dispersion relation E-N (q) for the spin-spiral of monolayer CoI2 without SOC and the energy dispersion relation EN+S (q) considering SOC by using the generalized Bloch condition combined with the spin-spiral method. The parameters of the E-s (q) Heisenberg exchange interaction induced by the SOC are obtained by fitting the dispersion law of the 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 the monolayer CoI2, where Gamma(1) reaches 1.09 meV. We predict that the Kitaev interactions are universally applicable to transition metal triangular lattices with 1T structure. It is shown that the CoI2 can be used as an alternative material for Kitaev and lays a theoretical foundation for exploring Kitaev interactions in other 2D magnetic materials.