Exciton Condensation in a Holographic Double Monolayer Semimetal
  The formation of intra-layer and inter-layer exciton condensates in a model of a double monolayer Weyl semi-metal is studied in the strong coupling limit using AdS/CFT duality. We find a rich phase diagram which includes phase transitions between inter-layer and intra-layer condensates as the charge densities and the separation of the layers are varied. The tendency to inter-layer condensation is strongest when the charge densities are balanced so that the weak coupling electron and hole Fermi surfaces would be nested. For systems with multiple species of massless Fermions, we find a novel phase transition where the charge balance for nesting occurs spontaneously. 
Gianluca Grignani, Andrea Marini, Namshik Kim, Gordon W. Semenoff
hep-th cond-mat.str-el