Strongly chiral correlated second-order nonlinear optical effects in two-dimensional van der Waals In4/3P2Se6 nanosheets

We report a novel, to our knowledge, two-dimensional (2D) material, In_4/3P₂Se₆, synthesized by the chemical vapor transport (CVT). Under 1064 nm laser excitation, In_4/3P₂Se₆ exhibits exceptional second-harmonic generation (SHG) intensity twice that of monolayer molybdenum disulfide (MoS₂). Furthermore, its intrinsic chirality and asymmetric centers facilitate strong interactions with circularly polarized light (CPL), resulting in pronounced second-harmonic generation circular dichroism (SHG-CD). At a thickness of 55 nm, the SHG-CD anisotropy factor reaches 0.639. The tunable nonlinear geometrical phase in this material presents new opportunities for next-generation nonlinear photonic devices.