Giant enhancement of optical nonlinearities in hybrid WS2/plasmon structures probed by ultrafast two-dimensional electronic spectroscopy (Invited Paper)

Transition metal dichalcogenide (TMDC) monolayers are quantum materials with unusual optoelectronic properties. Strongly bound excitons in the material are particularly sensitive to many-body interactions in the atomically thin monolayer, dominating their optical nonlinearity. Hybridization of these excitons with light-like excitations, such as surface plasmon polaritons (SPPs), allows to dramatically alter the optical response and to tailor material properties on the nano scale . The role of excitonic many-body interactions for the new hybridized polariton states is of crucial importance. The ideal tool to investigate these interactions and their coherent dynamics is ultrafast two-dimensional electronic spectroscopy (2DES). Here, we report the first ultrafast 2DES spectra of a TMDC monolayer coupled to plasmonic nanoresonator array. We show that the coupling between excitons and plasmons large enhances the nonlinearity of the hybrid system, exceeding that of the individual exciton and plasmon subsystems by more than an order of magnitude. Our results demonstrate that many-body effects on the two-quantum excitations play a crucial role for this nonlinearity enhancement.