Formation of moire interlayer excitons in space and time

Moire superlattices in atomically thin van der Waals heterostructures hold great promise for extended control of electronic and valleytronic lifetimes(1-7), the confinement of excitons in artificial moire lattices(8-13) and the formation of exotic quantum phases(14-18). Such moire-induced emergent phenomena are particularly strong for interlayer excitons, where the hole and the electron are localized in different layers of the heterostructure(19,20). To exploit the full potential of correlated moire and exciton physics, a thorough understanding of the ultrafast interlayer exciton formation process and the real-space wavefunction confinement is indispensable. Here we show that femtosecond photoemission momentum microscopy provides quantitative access to these key properties of the moire interlayer excitons. First, we elucidate that interlayer excitons are dominantly formed through femtosecond exciton-phonon scattering and subsequent charge transfer at the interlayer-hybridized sigma valleys. Second, we show that interlayer excitons exhibit a momentum fingerprint that is a direct hallmark of the superlattice moire modification. Third, we reconstruct the wavefunction distribution of the electronic part of the exciton and compare the size with the real-space moire superlattice. Our work provides direct access to interlayer exciton formation dynamics in space and time and reveals opportunities to study correlated moire and exciton physics for the future realization of exotic quantum phases of matter.

Automated summary

Moire superlattices in van der Waals heterostructures can generate interlayer excitons with unique physical properties. By using femtosecond photoemission momentum microscopy, the formation mechanism and wavefunction distribution of interlayer excitons are quantitatively studied, providing insights for the investigation of correlated moire and exciton physics.