Nonlinear Optical Properties of Transition Metal Dichalcogenide MX2 (M = Mo, W; X = S, Se) Monolayers and Trilayers from First-principles Calculations
Abstract
Due to the absence of interlayer coupling and inversion symmetry, transition metal dichalcogenide (MX2) semiconductor monolayers exhibit novel properties that are distinctly different from their bulk crystals such as direct optical band gaps, large band spin splittings, spin-valley coupling, piezoelectric and nonlinear optical responses, and thus have promising applications in, e.g., opto-electronic and spintronic devices. Here we have performed a systematic first-principles study of the second-order nonlinear optical properties of MX2 (M = Mo, W; X = S, Se) monolayers and trilayers within the density functional theory with the generalized gradient approximation plus scissors correction. We find that all the four MX2 monolayers possess large second-order optical susceptibility (2) in the optical frequency range and significant linear electro-optical coefficients in low frequency limit, thus indicating their potential applications in non-linear optical devices and electric optical switches. The (2) spectra of the MX2 trilayers are overall similar to the corresponding MX2 monolayers, albeit with the magnitude reduced by roughly a factor of 3. The prominent features in the (2) spectra of the MX2 multilayers are analyzed in terms of the underlying band structures and optical dielectric function, and also compared with available experiments.