Executive Summary : | This project proposal aims to investigate the valley Hall effect in semiconducting transition metal dichalcogenides (TMDC) van der Waal heterostructure at room temperature under an out of the plane electric field. TMDCs have direct band gaps in monolayer at K and K' points in the Brillouin zone and valley polarized emission. Circularly polarized incident light can create a valley imbalance in TMDCs, which has a short lifetime of the order of ps. Forming an interlayer exciton with TMDC heterostructure increases the lifetime to the order of ns. For an interlayer exciton, the electron resides in one TMDC and the hole resides in the other TMDC, resulting in a permanent dipole moment pointing out of the sample plane. The emission of interlayer exciton can be tuned with an electric field applied perpendicular to the sample plane. Additionally, stacking one TMDC on top of another results in a moiré superlattice, whose period depends on the angle between the two TMDCs. The valley Hall effect has been experimentally observed in monolayer MoS2 at cryogenic temperatures, where an applied bias created the potential gradient. In bilayer MoS2, an electric field perpendicular to the plane of bilayer MoS2 broke the inversion symmetry in bilayer, necessary for the observation of valley Hall effect. In 2020, the valley Hall effect was observed at room temperature for interlayer exciton in TMDC heterostructure MoS2/WSe2. The project proposal aims to use TMDC heterostructure to observe the valley Hall effect at room temperature and further control it using an out of the plane electric field. |