Excitons in semiconductor moire superlattices

This Review discusses the recent progress in the emerging field of exciton phenomena in semiconductor moire superlattices. Semiconductor moire superlattices represent a rapidly developing area of engineered photonic materials and a new platform to explore correlated electron states and quantum simulation. In this Review, we briefly introduce early experiments that identified new exciton resonances in transition metal dichalcogenide heterobilayers and discuss several topics including two types of transition metal dichalcogenide moire superlattice, new optical selection rules, early evidence of moire excitons, and how the resonant energy, dynamics and diffusion properties of moire excitons can be controlled via the twist angle. To interpret optical spectra, it is important to measure the energy modulation within a moire supercell. In this context, we describe a few scanning tunnelling microscopy experiments that measure the moire potential landscape directly. Finally, we review a few recent experiments that applied excitonic optical spectroscopy to probe correlated electron phenomena in transition metal dichalcogenide moire superlattices.