Theoretical study of orbital magnetization and axion coupling in CoNb₃S₆andCoTa₃S₆

Both CoNb₃S₆ and CoTa₃S₆ have intercalated Co ions between NbS₂ layers and can exhibit a large anomalous Hall conductivity (AHC) due to the finite spin chirality obtained from the noncoplanar 3q Co spin configuration. This large AHC is originated from the effective magnetic field induced by the large Berry curvature of this noncollinear spin structure. When this spin chirality at each Co layer exhibits an opposite sign and the total AHC can be exactly cancelled out although each layer can have a finite AHC. Here, we show that a perturbation such as the electric field can generate the finite orbital magnetization coupled to the large Berry curvature and suggest the plausible axion coupling in these materials. We will discuss how we can quantify the axion coupling under finite electric or magnetic fields and modify the coupling strength via the material engineering using first-principles calculations.