Strong Coulomb interactions in single-layer transition metal dichalcogenides (TMDs) result in the emergence of strongly bound excitons. These excitons and excitonic complexes, trions or biexcitons, for example, possess the valley degree of freedom and can be either optically bright or dark, depending on the spin configuration of the conduction and valence bands. In this talk, I will review our recent efforts on probing and controlling excitons in monolayer MoSe2 and WSe2 TMDs with high magnetic fields.

By employing high-field optical magneto-spectroscopy under strong out-of-plane magnetic fields and as a function of doping level, we can identify different exciton species and deduce their valley origins and binding energies. When a strong magnetic field is applied parallel to the 2D plane, it can be used to tilt and mix the CB spin component of excitons, which allows us to brighten and probe directly otherwise optically dark excitons.