Topological valleytronics in 2D Transition Metal Dichalcogenides Semiconductors

In many crystals the Bloch bands have inequivalent and well separated energy extrema in the momentum space, known as valleys. The valley index constitutes a well-defined discrete degree of freedom for low-energy carriers that may be used to encode information. This has led to the concept of valleytronics, a new type of electronics based on manipulating the valley index of carriers. In the first part of this talk, I will describe a general scheme based on inversion symmetry breaking to control the valley index, using graphene and monolayers of MoS2 as an example. In particular, the valley Hall effect and valley-dependent optical selection will be discussed. In the second part, I will discuss the Berry phase effect on excitons formation and dynamics.