Valleytronics using light, electric fields and heat in 2D transition metal dichalcogenides

In the monolayer limit, two dimensional (2D) transition metal dichalcogenides (2H-MX₂, with M=Mo, W and X=S, Se) are semiconductors with a sizeable (1-2 eV) and direct electronic bandgap as well as (degenerate) valleys at the K+/K- corners of the Brillouin zone. Beyond their use as classical semiconductors, this peculiar electronic structure opens new and exciting possibilities for information processing that exploit the quantum degree of freedom known as the valley index. This emergent field of research is known as « valleytronics ». The valley degree of freedom is known to be more robust than the spin one. It has been established that K+/K- valleys can be selectively addressed by using circularly polarized light and electric fields by the valley Hall effect that allows resolving the valley polarization of charge carriers. More recently, we could show that temperature gradients also allow resolving the valley polarization through the valley Nernst effect (article under review in Nature Nanotechnology). The purpose of this master 2 internship is to generate and detect pure valley currents in WSe₂ using either electric fields or the absorption of circularly polarized light or both. The interplay between the valley degree of freedom and temperature gradients will be studied during the PhD.

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