Angular Engineering Strategy for Enhanced Surface Nonlinear Frequency Conversion in Centrosymmetric Topological Semimetal HfGe_0.92Te

Abstract Surface nonlinear optics are essential for developments in integrated photonics and micro/nano optoelectronics. However, the nonlinear optical conversion efficiency on a surface is restricted by the finite nonlinear susceptibility of matter and the intrinsic atomic‐layered interaction length between light and matter. In this work, based on an angular engineering strategy, it is demonstrated that the centrosymmetric topological semimetal HfGe_0.92Te crystal has a giant and anisotropic surface second‐order nonlinear susceptibility up to 5535 ± 308 pm V⁻¹ and exhibits efficient and unprecedented second‐harmonic generation (SHG). The maximum optical conversion efficiency is found to be up to 3.75‰, which is 10⁴ times higher than that obtained from a silicon surface. Because of the linear dispersion over a wide range of energies around the Dirac points, this high conversion efficiency can be maintained with SHG wavelengths ranging from the visible region (779 nm) to the deep‐UV region (257.5 nm). This study can facilitate the development of topological photonics and integrated nonlinear photonics based on topological semimetals.