Sliding Modulation in Nonlinear Optical Effect in Two-Dimensional van der Waals Cu 2 MoS 4 .

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., MoS 2 ). Based on first-principles calculations, in this study, we discover that layered Cu 2 MoS 4 with two tetrahedral [MoS 4 ] and [CuS 4 ] 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 MoS 2 with a single octahedral [MoS 6 ] motif because of different synergistic effects among intra- and interlayer NLO polarizations induced by the [CuS 4 ] and [MoS 4 ] NLO-active motifs. Furthermore, the Cu 2 MoS 4 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.