Unveiling Ultrafast Exciton Polariton Dynamics in Large-Area van der Waals Superlattices

The discovery and large-area synthesis of two-dimensional (2D) materials with controlled thickness, composition, and crystal quality open up a much wider range of possibilities for the hetero-integration of novel and multi-functional photonic platforms. In this work, we develop 2D chalcogenide materials, assemble them into superlattices with oxide materials, and investigate the strong light-matter interaction in this novel materials platform. The large-area superlattices were grown via artificial layering of the Al₂O₃ and monolayer WS₂.¹ The monolayer WS₂ can keep the direct bandgap properties to serve as an efficient emitter at a center wavelength of 611 nm. We performed the angle-dependent transient absorption spectroscopy (TAS) measurement to determine the carrier dynamics in the WS₂/Al₂O₃ superlattices (N= 5) coupled with a waveguide cavity. By using the femtosecond time-resolved pump-probe TAS, we obtain the strong light-matter interaction induced upper (568 nm) and lower (629 nm) exciton-polaritons splitting in the designed WS₂/Al₂O₃ superlattices at a large incident angle of 80 degrees under TE polarized light. In addition, we observed ultrafast lifetime of upper exciton-polaritons reduced from 1 picosecond to 0.6 picosecond with an increase probe angle. Moreover, we found the quasiparticle competition behavior between the upper and lower exciton-polaritons, and there has a significant nonlinear effect can be observed. In the end, we will discuss the working mechanism of the carrier dynamics in large-area superlattices coupled with a waveguide cavity and the outlook for van der Waals superlattices.<br/><br/>1. Kumar, P.<i> et al.</i> Light–matter coupling in large-area van der Waals superlattices. <i>Nature Nanotechnology</i> <b>17</b>, 182-189, doi:10.1038/s41565-021-01023-x (2022).