Anomalous Exciton-Condensation in Graphene Bilayers

In ordinary semiconductor bilayers, exciton condensates appear at total Landau level filling factor $ν_{T}=1$. We predict that similar states will occur in Bernal stacked graphene bilayers at many non-zero integer filling factors. For $ν_{T} = -3,1$ we find that the superfluid density of the exciton condensate vanishes and that a finite-temperature fluctuation induced first order isotropic-smectic phase transition occurs when the layer densities are not balanced. These anomalous properties of bilayer graphene exciton condensates are due to the degeneracy of Landau levels with $n=0$ and $n=1$ orbital character.

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