Brightening the Interlayer Excitons in Rhombohedral-Stacked Bilayer MoS₂

Interlayer excitons in two-dimensional transition metal dichalcogenides are long-lived optical excitations where electrons and holes reside in different layers with an electrostatic dipole across the van der Waals gap. Interlayer excitons' energy can be significantly tuned by electric fields, making them a great platform for studying various excitonic and other many-body phenomena. Due to their small oscillator strengths, most studies have focused on studying interlayer excitons through emitted photoluminescence. Here we report that multiple interlayer excitons in rhombohedral-stacked bilayer MoS₂ can be electrically brightened in reflection contrast spectra after they become resonant and hybridize with intralayer excitons. Since Berry phase winding provides additional azimuthal angular momenta in K valleys, distinct optical selection rules are observed in these hybridized species. Furthermore, the broken mirror symmetry in R-stacked bilayers allows us to identify the origin of these interlayer excitons and their coupling mechanisms.