Anisotropic Raman scattering and intense broadband second-harmonic generation in tellurium nanosheets.

Tellurium (Te) is a novel elementary material, which has recently attracted extensive attention due to its intriguing physical properties, such as topological, thermoelectric, and photoelectric properties. Further study on Te crystal structures will help to understand its properties and facilitate its application. Here, the angle-resolved polarized Raman spectroscopy has been employed to study Te crystal symmetry. Three different Raman vibration modes were obtained, each of which possess a different polarization dependence. Furthermore, it is revealed that Te nanosheets show a second-order harmonic response over a wide spectrum and have the greatest conversion efficiency at an excitation wavelength of 880 nm. Its second-order nonlinear susceptibility is estimated to be 2049. This substantial nonlinear optical response endows Te nanosheets with the potential for developing nonlinear photonic and optoelectronic nanodevices with high efficiency.