Structural Symmetry-Breaking-Driven Giant Optical Second Harmonic Generation in Janus Monolayer ReSSe

Abstract

Structural symmetry-breaking plays a crucial role in determining the second harmonic generation (SHG) intensity and pattern for two-dimensional (2D) materials. Herein, we report that the giant optical SHG can be achieved by designing a Janus structure for ReS 2 and ReSe 2 . The designing of a Janus ReSSe monolayer structure can break both the in-plane and out-of-plane symmetry of monolayer ReS 2 and ReSe 2, resulting in the occurrence of larger second-order nonlinear coefficients in the in-plane ( d 11, d 16, d 21, and d 22 ) and out-of-plane ( d 15 and d 31 ) components. The second-order nonlinear coefficient dispersion properties for the asymmetric Janus ReSSe monolayer give rise to a multifaceted dependence of the SHG on the azimuthal and polarization angles at different incident wavelengths including double and quadruple symmetries, rotation of polar axis, and variations in intensity. These results highlight the potential to deterministically engineer novel nonlinear optical properties in the designing of the Janus structure based on layered materials.