Charge and spin dynamics in two-dimensional semiconductors

Abstract

Two-dimensional (2D) layered materials have opened one of the most promising areas in solid-state physics, as they provide a broad range of physical phenomena in the nanoscale, suitable for applied and fundamental physics. Semiconducting transition metal dichalcogenides (TMDs) are among the most studied layered materials due to their direct bandgap character with robust excitonic properties. Moreover, their strong spin-orbit coupling provides these materials with rich spin-related physics that can be explored in fields like opto-spintronics. In this thesis, we optically study the charge and spin dynamics of semiconducting TMDs when in contact with gallium arsenide (GaAs) substrates and when applying an external magnetic field. We found that when semiconducting TMDs are placed on GaAs there is a charge transfer between them. This can result in the dissociation or full transfer of the excitons from one material to the other, which can be controlled by choosing the doping of the substrate, or by using different TMDs such as MoS2 or WSe2. Furthermore, we study the spin dynamics of monolayer MoSe2 under an external magnetic field perpendicular to the sample plane. We observe that the magnetic field can effectively control the spin dynamics in the monolayer, in agreement with a fast hole transfer between the valley states present in this material. Therefore, our results provide initial benchmarks on the charge and spin dynamics in 2D semiconductors, depending on their substrate and applied magnetic fields, which can enable their application in novel devices.