Every-other-layer Dipolar Excitons in a Spin-Valley locked Superlattice

In 2H stacked pristine multilayer transition metal dichalcogenides, the spin-valley locking effect yields an electronic superlattice structure, where alternating layers correspond to barrier and quantum well respectively, conditioned on the spin-valley indices. We show that the spin-valley locked superlattice hosts a new kind of dipolar excitons with the electron and hole constituents separated in an every-other-layer configuration. Such excitons become optically bright via hybridization with intralayer excitons, displaying multiple anti-crossing patterns in optical reflection spectrum as the dipolar exciton is tuned through the intralayer resonance by electric field. The reflectance spectra also reveal an excited state orbital of the every-other-layer exciton, pointing to a sizable binding energy in the same order of magnitude as the intralayer exciton. As layer thickness increases, the dipolar exciton can form one-dimensional Bose-Hubbard chain displaying a layer number dependent fine-structures in the reflectance spectra.