Slow Light in a 2D Semiconductor Plasmonic Structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons (SPPs) interacting with excitons in a semiconductor monolayer layer. Here, we use coupled exciton-SPPs in monolayer WSe2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear Exciton-Surface Plasmon Polariton (E-SPP) response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 10⁵ m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.