Nonlinear Optical Properties of Transition Metal Dichalcogenide MX$_2$ (M = Mo, W; X = S, Se) Monolayers and Trilayers from First-principles Calculations

TL;DR

This study uses first-principles calculations to analyze the second-order nonlinear optical properties of monolayer and trilayer transition metal dichalcogenides MX$_2$, revealing their strong potential for nonlinear optical applications.

Contribution

It provides a systematic first-principles analysis of the nonlinear optical susceptibilities of MX$_2$ monolayers and trilayers, highlighting their large $ ext{chi}^{(2)}$ and potential in optoelectronic devices.

Findings

All four MX$_2$ monolayers have large $ ext{chi}^{(2)}$ in the optical range.

Trilayers have similar $ ext{chi}^{(2)}$ spectra to monolayers but reduced by about a factor of 3.

$ ext{chi}^{(2)}$ spectra are explained by band structures and dielectric functions.

Abstract

Due to the absence of interlayer coupling and inversion symmetry, transition metal dichalcogenide (MX$_2$) 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 MX$_2$ (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 MX$_2$ monolayers possess large second-order optical susceptibility $\chi^{(2)}$ 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 $\chi^{(2)}$ spectra of the MX$_2$ trilayers are overall similar to the corresponding MX$_2$ monolayers, {\it albeit} with the magnitude reduced by roughly a factor of 3. The prominent features in the $\chi^{(2)}$ spectra of the MX$_2$ multilayers are analyzed in terms of the underlying band structures and optical dielectric function, and also compared with available experiments.