Circular Dichroism in Centrosymmetric Material without Optical Absorption

Controlling the spin degree of freedom is a vital step for achieving success in semiconductor spintronics. Remarkably, the layered transition metal dichalcogenides have been in the spotlight because of their ability to link spin and valley excitons with circularly-polarized light. However, current theories of spin-valley coupling or the corresponding induced spin-polarized photocurrents are founded on exciting real carriers which are above the bandgap. The question remains whether the excitation below the bandgap will yield the pertinent circular dichroism characteristics. In addition, identifying appropriate material platforms and effective detection approaches is a difficult challenge. Herein, utilizing elliptically terahertz emission spectroscopy, we investigate the ultrafast nonlinear physical responses in the centrosymmetric vertically-grown SnS2 material without optical absorption. We discover that the terahertz wave emitted from SnS2 exhibits a significant circular dichroism when the chirality of pump light is switched, indicating that spin polarization can be controlled without optical absorption. Our research has revealed a successful approach to the essential spin-related physical phenomena of other novel functional materials, and has highlighted the immense potential of terahertz spectroscopy technology in advanced science.