Behavior of electrons at low temperatures and in low dimensions


Nanostructures such as quantum point contacts and quantum dots, in combination with locally applied DC-to-microwave electric and magnetic fields, have enabled exquisitely detailed probes of their host materials, from GaAs heterostructures to carbon nanotubes and many others. These nanostructures provide highly tunable control over system parameters including size, shape, lateral position, exchange and spin-orbit energies, coupling to external reservoirs, and carrier density at the level of a single charge. 

Nanoscale confinement by local electrostatic gating leverages the band gap of 2D semiconductors to create nanostructures that are difficult or impossible to fabricate in gapless graphene.  Stacking 2D materials provides a convenient method for the assembly of high-quality nanostructures based on transition metal dichalcogenides and other layered materials. 

An initial target of these experiments will be to explore the valley pseudospin degree of freedom in transition metal dichalcogenides.  The energy bands of semiconducting transition metal dichalcogenides such as MoS2 and WSe2 possess the same valley structure as graphene, with the lowest lying bands located at the vertices of the hexagonal Brillouin zone (K and Kpoints). We will explore methods to create, manipulate, and measure populations of the valley pseudospin degree of freedom (K or K) provided by this band structure. In the same way that a spintronic device operates on the spin angular momentum of electrons rather than their charge, a valleytronic device operates on the crystal momentum associated with each valley.