Valley-polarized exciton currents in a van der Waals heterostructure

Valleytronics is an appealing alternative to conventional charge-based electronics which aims at encoding data in the valley degree of freedom, i.e. the information over which extreme of the conduction or valence band carriers are occupying. The ability to create and control valley-currents in solid state devices could therefore enable new paradigms for information processing. Transition metal dichalcogenides (TMDCs) are a promising platform for valleytronics, due to the presence of two inequivalent valleys with spin-valley locking(1) and a direct band gap(2,3), which allows optical initialization and readout of the valley-state(4,5). Recent progresses on the control of interlayer excitons in these materials(6–8) could offer an effective way to realize optoelectronic devices based on the valley degree of freedom. Here, we show the generation and transport over mesoscopic distances of valley-polarized excitons in a device based on a type-II TMDC heterostructure. Engineering of the interlayer coupling results in enhanced diffusion of valley-polarized excitons, which can be controlled and switched electrically. Furthermore, using electrostatic traps, we can increase exciton concentration by an order of magnitude, reaching densities in the order of 10(12) cm(-2), opening the route to achieving a coherent quantum state of valley-polarized excitons via Bose-Einstein condensation.