Nanoscale chiral valley-photon interface through optical spin-orbit coupling

The emergence of two-dimensional transition metal dichalcogenide materials has sparked intense activity in valleytronics, as their valley information can be encoded and detected with the spin angular momentum of light. We demonstrate the valley-dependent directional coupling of light using a plasmonic nanowire-tungsten disulfide (WS2) layers system. We show that the valley pseudospin in WS2 couples to transverse optical spin of the same handedness with a directional coupling efficiency of 90 +/- 1%. Our results provide a platform for controlling, detecting, and processing valley and spin information with precise optical control at the nanoscale.