Defesa de Tese de Doutorado #421 – Rafael Ricardo Rojas Lopez – 03/10/2023

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 a 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 a external magnetic field. Traditional semiconductors such as GaAs have a large interest as they are present in many opto-electronic devices and can be used to confine radiation. We found that when semiconducting TMDs are placed on GaAs there is a charge transfer between them. The latter can result in the dissociation of the generated excitons or in a full transfer of the excitons from one material to the other. This can be effectively controlled by properly 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 when applying an external magnetic field perpendicular to the plane of the sample surface. We observe that the magnetic field can effectively control the spin accumulation in the monolayer, which is 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.

Transmissão ao vivo no link:

https://www.rug.nl/about-ug/latest-news/events/promoties/digital-phd-ceremony