Intervalley Quantum Coherence Transfer and Coherently-Induced Chiral Plasmon Fields in WS2-Metallic Nanoantenna Systems

We theoretically show that when a hybrid system consisting of a transition metal dichalcogenide monolayer (WS2) and an achiral metallic nanoantenna interacts with a circularly polarized laser field, plasmonically mediated coherently induced processes can transfer quantum coherence from one valley (K or K') to another. This leads to spin-valley-dependent plasmon field enhancement and coherently driven energy transfer from the WS2 monolayer to the nanoantenna. For the case when the incident laser is right circularly polarized (sigma(+)), we study intervalley transfer of excitation and polarization from K to K' valleys while mapping the evolution of the Stokes vectors associated with the emission of the WS2 monolayer. This is done as we explore the impact of variation of the laser frequency and intensity on K-K' coupling. Our results show a formation of collective quantum states and an abrupt transition between these states at a certain frequency. We demonstrate that, as such a transition happens, the Stokes vector follows a unique trace that depicts a large degree of control over the valley quantum coherence. This includes an abrupt change in the valley coherent superposition, which causes an outburst of energy transfer from the WS2 monolayer to the nanoantenna.