NbOBr₂ (Niobium Oxydibromide)

A niobium oxyhalide layered van der Waals material with strong in-plane structural anisotropy. Its intrinsic polar (non-centrosymmetric) lattice endows it with a pronounced second-order nonlinear optical response, making it a recently discovered, highly efficient candidate for two-dimensional nonlinear optics and quantum light sources, capable of generating entangled photon pairs. Its quasi-one-dimensional chain structure further gives rise to anisotropic electrical and optical properties, establishing it as an emerging platform for low-dimensional polar materials and nonlinear photonics.