  Valley selective hybridization and residual coupling of electronic states in
commensurate van der Waals heterobilayers enable the control of the orbital
character of interlayer excitons. We demonstrate electric field control of
layer index, orbital character, lifetime and emission energy of indirect
excitons in MoS2/WS2 heterobilayers embedded in an vdW field effect structure.
Different excitonic dipoles normal to the layers are found to stem from bound
electrons and holes located in different valleys of MoS2/WS2 with a valley
selective degree of hybridization. For the energetically lowest emission lines,
coupling of electronic states causes a field-dependent level anticrossing that
goes along with a change of the IX lifetime from 400 ns to 100 ns. In the
hybridized regime the exiton is delocalized between the two constituent layers,
whereas for large positive or negative electric fields, the layer index of the
bound hole is field-dependent. Our results demonstrate the design of novel van
der Waals solids with the possibility to in-situ control their physical
properties via external stimuli such as electric fields.
