Mott-Enhanced Exciton Condensation in a Hubbard bilayer

TL;DR

This paper investigates the conditions under which excitonic condensation occurs in a Hubbard bilayer system, revealing the role of Mott localization and inter-layer interactions through advanced theoretical modeling.

Contribution

It demonstrates the stability of excitonic phases in a Hubbard bilayer, highlighting the influence of Mott localization and inter-layer interactions, with a comprehensive theoretical characterization.

Findings

Excitonic phase stable over a broad phase diagram region.

Inter-layer interaction V promotes excitonic phase, especially when V > U.

Large U extends excitonic stability even when U > V due to Mott localization.

Abstract

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 sizeable region of a phase diagram spanned by the intra-layer (U) and inter-layer (V) interactions. The latter term is expected to favour 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 naive expectations. The extended stability of the excitonic phase can be linked to in-layer Mott localization and inter-layer spin correlations. Using a mapping to a model with attractive inter-layer coupling, we fully characterize the condensate phase in terms of its superconducting counterpart, thereby addressing its coherence and correlation length.