Symmetric Interlayer Trions in 3 <i>R</i> - and 2 <i>H</i> -Stacked MoS ₂ Bilayers

Transition metal dichalcogenide (TMD) semiconductors host intriguing excitonic physics due to their large exciton binding energies and high oscillator strengths. These materials can be further engineered into heterostructures to realize a variety of exciton configurations. In type-II band alignment heterobilayers, dipolar interlayer excitons can form, with the electron and hole residing in separate layers. Additionally, moiré patterns can create superlattice potentials that localize excitons. In this study, we present a novel type of exciton structure observed in naturally stacked 3R- and 2H-MoS2 bilayers. When the compound is subjected to an external electric field, a transition from dipolar, negatively charged interlayer trions (IX–) to symmetric IX– is observed. This is identified by a sudden increase in photoluminescence intensity and a red shift in the peak position. Especially, the spontaneous polarization field inherent in 3R-MoS2 bilayers results in sequential electron filling between the top and bottom layers, allowing direct observation of the IX– structure transition with electron doping. The field-tunable IX– species in MoS2 bilayers offer a unique and robust platform for investigating exotic excitonic interactions and related quantum states.