Time- and spatially-resolved optical spectroscopy of MoS2 monolayers

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We propose to investigate the properties of monolayers of the compound semiconductor MoS2 using various optical spectroscopy techniques. MoS2, like graphite, is a material with a pronounced layer structure, where individual layers are strongly bound by covalent bounds, while interlayer coupling is mediated by weak van der Waals forces. Bulk MoS2 is an indirect-gap semiconductor. However, it was demonstrated in 2010 that it shows pronounced photoluminescence if it is thinned to a single layer, and DFT calculations predict a direct bandgap for a monolayer. Conduction and valence band states in MoS2 are formed from d-like Mo orbitals, in stark contrast to the s- and p-like states in III-V semiconductors. We want to investigate the band structure of MoS2 using photoluminescence and photoluminescence excitation at low temperatures and in high magnetic fields. A direct consequence of the crystal structure of MoS2 monolayers is the coupling between spin and valley degrees of freedom, which should lead to new opto-electronic effects, such as the Valley Hall effect. We propose to study the carrier, spin and valley dynamics in MoS2 monolayers in time- and spatially-resolved optical experiments in order to observe the predicted effects.