Cooper-like instability in an excitonic insulator

We explore the crossover from weak to strong correlations in Dirac materials for the excitonic insulator transition in a paradigmatic family of ‘slow’ graphene, i.e. graphene with renormalized bands. Two different models are considered, contrasting a mean-field model with a Bethe-Salpeter calculation. Our analysis reveals competition between condensation of q=0 and q = (pi,0) excitons, with the latter splitting the Van Hove singularities of the graphene bands.