Optical and plasmonic spectroscopy of 2D semiconductor heterostructures*

Over the past decade, there has been significant interest in the optical and electronic physics of semiconducting transition metal dichalcogenide (TMD) monolayers and heterostructures. TMD monolayers are known to host strongly bound excitons at the K and –K valleys on the edge of the Brillouin zone, which exhibit a strong nonlinear optical response. In this presentation, I will discuss how TMD monolayers can be integrated in plasmonic waveguide structures to realize a coupled exciton-surface plasmon polariton that exhibits an enhanced nonlinear response, including coherent population oscillations of excitons. Furthermore, two different TMD monolayers, such as MoSe₂ and WSe₂, can be stacked together to realize a type-II heterojunction that hosts interlayer excitons. The interlayer exciton transitions are optically bright if the heterostructure twist angle is near 0° or 60°; however, these two types of heterostructures (i.e., near 0° vs. near 60°) exhibit different interlayer K valley alignments. I will discuss the impact of the band alignments on the moiré physics of the heterostructure and the interlayer exciton dynamics. These effects are probed with low temperature photoluminescence and nonlinear optical spectroscopy.