  The robust spin and momentum valley locking of electrons in two-dimensional
semiconductors make the valley degree of freedom of great utility for
functional optoelectronic devices. Owing to the difference in optical selection
rules for the different valleys, these valley electrons can be addressed
optically. The electrons and excitons in these materials exhibit valley Hall
effect, where the carriers from specific valleys are directed to different
directions under electrical or thermal bias. Here we report the optical valley
Hall effect where the light emission from the valley polarized excitons in
monolayer WS2 propagates in different directions owing to the preferential
coupling of excitonic emission to the high momentum states of the hyperbolic
metamaterial. The experimentally observed effects are corroborated with
theoretical modeling of excitonic emission in the near field of hyperbolic
media. The demonstration of the optical valley Hall effect using a bulk
artificial photonic media without the need for nanostructuring opens the
possibility of realizing valley-based excitonic circuits operating at room
temperature.
