Ultrafast dynamics of Bloch surface wave polaritons in large-area 2D semiconductor monolayers at room temperature.

The dynamics of strongly coupled polariton systems integrated with two-dimensional transition metal dichalcogenides (TMDs) is key to enabling efficient coherent processes and achieving high-performance TMD-based polaritonic devices such as ultralow-threshold polariton lasers and ultrafast optical switches. However, there has been a lack of a comprehensive understanding of the excited state dynamics in TMD-based polariton systems. In this work, we use ultrafast pump-probe optical spectroscopy to investigate the room-temperature dynamics of the polariton systems consisting of TMD monolayer excitons strongly coupled with Bloch surface waves (BSWs) supported by all-dielectric photonic structures. The transient response is found for both above-exciton energy pumping and polariton-resonant pumping. We observe the excited state population and ultrafast coherent coupling of the exciton reservoir and lower polariton (LP) branch for resonant pumping. Moreover, it is found that transient response of the LP first decays on a short time scale of 0.15-0.25 ps compared to the calculated intrinsic lifetime of 0.11-0.20 ps, and is followed by longer decay (> 100 ps) due to the dynamical evolution of the exciton reservoir. Our results provide a fundamental understanding of the dynamics in TMD-based polariton systems while showing the potential for achieving efficient coherent optical processes for device applications. This article is protected by copyright. All rights reserved.