Non-Centrosymmetric 2D Nb₃SeI₇ with High In-Plane Anisotropy and Optical Nonlinearity

Integrating anisotropy and nonlinearity of physical properties in 2D materials is of great importance to the progress of nanoelectronic, nanophotonic, and nano-optoelectronic applications. In this work, Nb₃SeI₇, a newly discovered ternary layered material with non-centrosymmetric lattices, is introduced, which exhibits strong second harmonic generation (SHG), in-plane anisotropic electricity, and light absorption. Symmetry breaking of 2D Nb₃SeI₇ induced by the polar off-center displacement of niobium leads to a high nonlinear optical response with a second-order susceptibility of 6.71 pm V⁻¹ and a high anisotropic factor of photoresponsivity up to 4.6, which are higher than most of the 2D materials. These properties of 2D Nb₃SeI₇ create new possibilities for chip-integrated nonlinear optics devices and future-proof polarization-sensitive optoelectronic systems.