Giant Stark splitting of an exciton in bilayer MoS₂

Transition metal dichalcogenides constitute a versatile platform for atomically thin opto-electronic devices.
We integrate homobilayer MoS₂ in a dual-gate device structure allowing independent control of the electron density and out-of-plane electric field [1]. On increasing the electric field at close-to-zero electron concentration, we observe two well-separated features in our absorption measurements: the energy degeneracy of the two interlayer exciton configurations is lifted. This result reveals a large in-built electric dipole. It is consistent with an interlayer character of the transition: the electron is localized in the top or the bottom layer, while the hole is delocalized across the bilayer. We tune the energy splitting between these two interlayer excitons by as much as 120 meV such that we are able to bring the interlayer excitons energetically close to resonance with the intralayer states. While the interaction with the intralayer A-exciton is weak, we observe an avoided crossing of the upper interlayer exciton with the intralayer B-exciton.
These highly tunable excitonic transitions with large oscillator strength hold great promise for non-linear optics with polaritons.

[1] N. Leisgang et al., Nature Nanotechnology (2020).