Interlayer coupling and gate-tunable excitons in transition metal dichalcogenide heterostructures

Bilayer van der Waals heterostructures such as MoS2/WS2 and MoSe2/WSe2 have attracted much attention recently, particularly because of their type II band alignments and the formation of interlayer exciton as the lowest-energy excitonic state. Here, we calculate the electronic and optical properties of such heterostructures with the first-principles GW+Bethe-Salpeter Equation method and reveal the important role of interlayer coupling in deciding the excited-state properties, including the band alignment and excitonic properties. Our calculation shows that due to the interlayer coupling, the low energy excitons can be widely tunable by a vertical gate field. In particular, the dipole oscillator strength and radiative lifetime of the lowest energy exciton in these bilayer heterostructures is varied by over an order of magnitude within a practical external gate field. Then we build a minimal model that captures the essential physics behind this tunability and allows the extension of the ab initio results into a larger range of electric fields.