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

However, the materials currently generally face challenges such as high toxicity, poor stability, and complex preparation processes. Here, a new two-dimensional (2D) In₄/₃P₂Se₆ was synthesized by chemical vapor transport (CVT) techniques, showing strong second harmonic generation (SHG) intensities twice that of monolayer MoS₂ when excited by a 1064 nm laser.

The SHG intensity has a strong dependence on the thickness and is optimal at a thickness of 7 nm. Additionally, these materials demonstrate intrinsic chirality and asymmetric centers, leading to interactions with circularly polarized light (CPL), which results in pronounced second harmonic generation circular dichroism (SHG-CD), with an anisotropy factor of 0.639 at the thickness of 55 nm. The tunable nonlinear geometrical phase offered by In₄/₃P₂Se₆ presents new opportunities for next-generation nonlinear photonic devices.