Title: Interlayer coupling and gate-tunable excitons in transition metal dichalcogenide heterostructures,
Abstract: Bilayer van der Waals (vdW) 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. In this work, we calculate the electronic and optical
properties of such heterostructures with the first-principles GW+Bethe-Salpeter
Equation (BSE) 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. We also build a
simple model that captures the essential physics behind this tunability and
allows the extension of the ab initio results to a large range of electric
fields. Our work clarifies the physical picture of interlayer excitons in
bilayer vdW heterostructures and predicts a wide range of gate-tunable
excited-state properties of 2D optoelectronic devices.