Abstract
Atomically thin group-VI transition metal dichalcogenides (TMDC) has been emerging as a family of intrinsic 2-dimensional (2D) crystals with a sizeable bandgap in the visible and near infrared range, satisfying numerous requirements for ultimate electronics and optoelectronics. This intrinsic 2D crystal also provides a perfect platform for physics study in 2D semiconductors. The characteristic inversion symmetry breaking presented in monolayer TMDCs leads to non-zero but contrasting Berry curvatures and orbit magnetic moments at K/K’ valleys located at the corners of the first Brillouin zone. These features provide an opportunity to manipulate electrons’ additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDC a promising candidate for the conceptual valleytronics. Besides, the strong spin-orbit interactions and the subsequent spin-valley coupling demonstrated in 2D TMDCs open potential new routes towards quantum manipulation.
Here, I present our progress of the physics study in tungsten disulfide (WS2) thin films via optical spectroscopy. Particularly, our experimental approach on the excitonic effect, valley dependent circular dichroism, and spin-valley coupling in monolayer and bilayer WS2 are introduced. By the result, enhanced Coulomb interaction, valley polarization and coherence, the interplay of spin, valley and layer degrees of freedom in WS2 thin films are also discussed.