Angular Dependence of the Second-Order Nonlinear Optical Response in Janus Transition Metal Dichalcogenide Monolayers

With advances in the growth of Janus transition metal dichalcogenide (TMD) monolayers and potential applications for materials with a permanent dipole moment, we investigate the electronic, linear, and second-order nonlinear optical properties of Janus TMDs using first-principles calculations. We compare our results to available experimental measurements, finding relatively good agreement. We find the appearance of Rashba spin splitting and the mixing of the second-order nonlinear susceptibility components in Janus TMD monolayers contrary to their TMD monolayer counterparts. While the Rashba effect is small, it does modify the electronic band structure near Γ, making Janus TMDs potentially useful for spintronic applications. In analyzing the mixing of the nonlinear optical susceptibility components, which depend on the angular orientation of the experimental setup and the frequency of the measurement, we find enhancement of the effective nonlinear susceptibility. Our elucidation of the susceptibility components of Janus TMD monolayers as dependent on the angular orientation in an experimental setup provides an understanding and interpretation of the second-order nonlinear response.