Mott-enhanced exciton condensation in a Hubbard bilayer

We study the conditions to realize an excitonic condensed phase in an electron-hole bilayer system with local Hubbard-like interactions at half-filling, where we can address the interplay with Mott localization. Using dynamical mean-field theory, we find that an excitonic state is stable in a sizable region of a phase diagram spanned by the intralayer (U) and interlayer (V) interactions. The latter term is expected to favor the excitonic phase which is indeed found in a slice of the phase diagram with V>U. Remarkably, we find that, when U is large enough, the excitonic region extends also for U>V, in contrast with naïve expectations. The extended stability of the excitonic phase can be linked to in-layer Mott localization and interlayer spin correlations. Using a mapping to a model with attractive interlayer coupling, we fully characterize the condensate phase in terms of its superconducting counterpart, thereby addressing its coherence and correlation length.