Magneto-optical properties in AA-stacked bilayer transition metal dichalcogenides under an exponentially decaying magnetic field

The Landau levels (LLs) and magneto-optical responses in the AA-stacked bilayer transition metal dichalcogenides in the presence of an exponentially decaying magnetic field are investigated. Sixteen separate Landau levels are predicted in the numerical results, which are the result of the spin, valley, and layer degeneracy lifting induced by the spin Zeeman field. Interestingly, we find that the ∇B drift velocity perpendicular to the magnetic field gradient is τ⋅s-degenerate and independent of the layer index and the strength of the spin Zeeman field. Based on the linear-response theory, the magneto-optical conductivity is derived as a function of photon energy where only the intraband transition associated with the incident light in the THz regime is considered. Our result reveals that the merit of absorption peaks in the real part of longitudinal conductivity under the nonuniform magnetic field is influenced by the combined effect of the optical transition selection rule and the mixing rule of Landau states. Moreover, the response of optical conductivity is significantly modified when the inhomogeneity of the magnetic field, i.e., ξ0, is varied. Furthermore, the position of optical response is found to shift toward the high magneto-excitation frequency as ξ0 increases.