Stark Shift Reveals Stacking-Dependent Dipole Orientations of Excitons in ReS ₂

The dipole moment and polarizability reveal important material properties of excitons in two-dimensional materials, which can be studied through the Stark shift. However, observing excitonic Stark shift requires a device design that enhances electric field coupling. Here, we demonstrate that a significant Stark shift in excitons can be observed in a back-gated field-effect transistor geometry with a specific layer stacking in rhenium disulfide (ReS 2 ). Structural stacking provides exceptional control over the excitonic response in these few-layer devices. AB-stacked ReS 2 shows the contribution of the linear and quadratic Stark shifts, approximately 13 meV, in the off-state of the transistor. In contrast, AA-stacked samples display negligible Stark shift, highlighting the stacking-dependent dipole moment of excitons in ReS 2 . Understanding the orientation of anisotropic excitons can be highly valuable for developing electronically tunable light–matter interactions and excitonic transport in optoelectronic devices.