  Recent advances in fabrication of two dimensional materials and their moir\'e
heterostructures have opened up new avenues for realization of ground-state
excitonic insulators, where the structure spontaneously develops a finite
interlayer electronic polarization. We propose and analyze a scheme where an
optically generated intralayer exciton is screened by excitations out of the
excitonic insulator to form interlayer polarons. Using Quantum Monte-Carlo
calculations we first determine the binding energy of the biexciton state
composed of inter- and intralayer excitons, which plays a central role in
understanding polaron formation. We describe the excitations out of the
ground-state condensate using BCS theory and use a single
interacting-quasiparticle-pair excitation Ansatz to describe dynamical
screening of optical excitations. Our predictions carry the hallmarks of the
excitonic insulator excitation spectrum and show how changing the interlayer
exciton binding energy by increasing the layer separation modifies the optical
spectra.
