Angular engineering for the enhancement of surface nonlinear frequency conversion in centrosymmetric topological semimetal HfGe0.92Te

Abstract Surface nonlinear optics lays at the heart of integrated photonics and micro-nano optoelectronics, whose efficiency is restricted by the finite nonlinear susceptibility of matter and the intrinsic atomic-layered interaction length between light and matter. Herein, we originally demonstrate that the centrosymmetric topological semimetal HfGe0.92Te crystal possesses a giant and anisotropic surface second-order nonlinear susceptibility up to 5535 ± 308 pm·V− 1 and manifests efficient and unprecedented second-harmonic generation (SHG) based on the angular engineering strategy. The maximum optical conversion efficiency is up to 3.75‰, a value that is 1015 orders of magnitude larger than the conventional surface SHG. Benefiting from the linear dispersion in a large energy range around the Dirac points, we find that this high conversion efficiency can be maintained with the SHG wavelengths ranging from the visible region to the deep ultraviolet one (515 nm-257.5 nm). Our work may open the door for the development of topological photonics and integrated nonlinear photonics based on topological semimetals.