NanoScience Colloquium by Prof. Paul van Loosdrecht from University of Cologne

The two-dimensionality of monolayers and heterostructures of transition-metal dichalcogenides lead to a reduced dielectric screening and consequently to relatively strongly bound excitons. 

Not surprisingly, these systems show a wealth of interesting exciton and optical physics phenomena, including the formation of trions, strong luminescence, and multi-exciton phenomena. One of the more intriguing phenomena is that the lack of inversion symmetry in these systems combined with a strong spin-orbit coupling yields a novel quantum mechanical degree of freedom, the valley pseudospin, which is interesting from a fundamental point of view and even has some application potential. 

In this presentation, I will highlight some of the properties of these novel materials as investigated by ultrafast techniques like transient absorption and transient grating spectroscopy, focusing on the pseudospin dynamics, interlayer charge and pseudospin transfer in heterostructures, and enhanced mobility due to interlayer screening effects.