Flatband excitons in a three-dimensional supertwisted spiral transition metal dichalcogenide

Twisted few-layer graphene and transition metal dichalcogenide (TMD) heterostructures are versatile platforms for studying strongly correlated electrons by the formation of tunable moiré bands. A frontier in this field is three-dimensional (3D) topological twistronics, where each successive layer rotates the same angle towards the bulk limit in a supertwisted assembly. Theoretical frameworks have predicted intriguing topological physics such as magic-angle Weyl fermions in supertwisted graphite. However, the electronic structure and excitonic behaviors of supertwisted TMD are barely explored. Here we reveal new types of excitons emerging from the flatbands in 3D supertwisted WS₂, where the supertwist narrows band edge dispersions in both 2D and 3D Brillouin zones, supporting distinctive and robust new excitonic transitions. Position-, temperature-, twist angle- and polarization-dependent photoluminescence (PL) studies unveils the new direct and indirect 3D excitons, in addition to the 2D excitons that resemble A excitons. Furthermore, polarimetry imaging enables direct visualization of the excitons spatial distribution and polarization properties. Both band structure and real-space local density-of-state (LDOS) calculations confirm the 2D and 3D flatbands with gaps, supporting the emergence of the observed excitons. The LDOS results further reveal super-moiré modulation and conform to a theory of squeezed quantum vortex states in spiral lattices.