  Ensembles of indirect or interlayer excitons (IXs) are intriguing systems to
explore classical and quantum phases of interacting bosonic ensembles. IXs are
composite bosons that feature enlarged lifetimes due to the reduced overlap of
the electron-hole wave functions. We demonstrate electric Field control of
indirect excitons in MoS2/WS2 hetero-bilayers embedded in a field effect
structure with few-layer hexagonal boron nitrite as insulator and few-layer
graphene as gate-electrodes. The different strength of the excitonic dipoles
and a distinct temperature dependence identify the indirect excitons to stem
from optical interband transitions with electrons and holes located in
different valleys of the hetero-bilayer featuring highly hybridized electronic
states. For the energetically lowest emission lines, we observe a
field-dependent level anticrossing at low temperatures. We discuss this
behavior in terms of coupling of electronic states from the two semiconducting
monolayers resulting in spatially delocalized excitons of the hetero-bilayer
behaving like an artificial van der Waals solid. Our results demonstrate the
design of novel nano-quantum materials prepared from artificial van der Waals
solids with the possibility to in-situ control their physical properties via
external stimuli such as electric fields.
