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

Chiral nonlinear optical properties have attracted great attention in the fields of optical cryptography, holographic imaging and quantum information processing. 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.