Field/valley plasmonic meta-resonances in WS2-metallic nanoantenna systems: Coherent dynamics for molding plasmon fields and valley polarization

We theoretically study spin-valley quantum coherence dynamics in a hybrid system consisting of a monolayer of transition metal dichalcogenide (WS2) and an Ag nanoantenna. For this we map the time evolution of the Bloch and Stokes vectors to investigate, respectively, the dynamics of valley excitons and the states of polarization of plasmon near fields. The results show the formation of two types of collective resonances in the time domain, i.e., valley and field plasmonic meta-resonances (VPMR and FPMR). VPMR is shown as a coherently time-delayed ultrafast rotation of the Block vector. FPMR, on the other hand, occurs as an abrupt change in the near-field polarization of the Ag nanoantenna. The "time of occurrence" (resonance time) of such meta-resonances can be tuned using the intensity and polarization of the laser field responsible for the excitation of the system. Our results show that FPMR can decorate near fields of the Ag nanoantenna at different locations with various types of coherent-field dynamics with nanoscale spatial resolution. VPMR, on the other hand, offers an avenue to control the spin-valley states of transition metal dichalcogenide monolayers using minuscule changes in the intensity and polarization of the incident light.