Nonlinear plasmonics with monolayer semiconductor excitons

The far-field linear and nonlinear optical response of excitons in two-dimensional (2D) semiconducting transitional metal dichalcogenides (TMDs), such as MoS₂ and WSe₂, have been the subject of intense investigation over the past decade. Here, we report on our experimental results measuring the linear and nonlinear response of surface plasmon polaritons (SPPs) propagating on metallic waveguides interacting with excitons in a single WSe₂ monolayer. The WSe₂ monolayer was encapsulated in hexagonal boron nitride and transferred on top of a metallic waveguide. The measurements were carried out at low temperature (below 11 K). We measured the linear absorption of SPPs by excitons, resulting in a 73 % attenuation of the transmitted probe. To determine the nonlinear response, we performed both optical pump-SPP probe and SPP pump-SPP probe experiments. For the SPP pump case, a differential transmission response exceeding 4 % was achieved. Time-resolved pump-probe measurements reveal a fast component of the nonlinear response of 290 fs with a slower 13.7 ps component, consistent with previous optical measurements. These plasmonic structures could open up new opportunities to probe fundamental light-matter interactions in 2D material-plasmonic heterostructures.