Sliding Modulation in Nonlinear Optical Effect in Two-Dimensional van der Waals Cu₂MoS₄

Abstract

Owing to different nonlinear optical (NLO) motifs with diverse structural and symmetrical assemblies, two-dimensional (2D) van der Waals (vdW) transition metal ternary chalcogenides (TMTCs) have unique advantages in nano-NLO modulation compared to 2D vdW transition metal dichalcogenides (e.g., MoS₂). Based on first-principles calculations, in this study, we discover that layered Cu₂MoS₄ with two tetrahedral [MoS₄] and [CuS₄] motifs, as a representative 2D vdW TMTC, has an extremely rare sliding-modulated second harmonic effect with nearly 70% fluctuation, much larger than 5% in MoS₂ with a single octahedral [MoS₆] motif because of different synergistic effects among intra- and interlayer NLO polarizations induced by the [CuS₄] and [MoS₄] NLO-active motifs. Furthermore, the Cu₂MoS₄ layers exhibit a low energy barrier in interlayer sliding with a robust SHG response against large strains, displaying a novel and applicable NLO-modulation mechanism in nano-optoelectronics.