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| VOLUME 87 | ISSUE 1 |
PAGE 61
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| Electron-hole pair condensation in graphene bilayer |
Yu. E. Lozovik, A. A. Sokolik
Institute of Spectroscopy, RAS, 142190 Troitsk, Moscow Region, Russia
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PACS: 73.21.Ac, 74.78.-w, 81.05.Uw
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Abstract
We consider the pairing of electrons and holes due to their
Coulomb attraction in two parallel, independently gated graphene layers,
separated by a barrier. At weak coupling, there exist the BCS-like
pair-condensed state. Despite
the fact that electrons and holes behave like massless Dirac fermions, the
problem of BCS-like electron-hole pairing in graphene bilayer turns out to be
rather similar to that in usual coupled semiconductor quantum wells. The
distinctions are due to Berry phase of electronic wave functions and
different screening properties. We estimate values of the gap in one-particle
excitation spectrum for different interlayer distances and carrier
concentrations. Influence of
disorder is discussed. At large enough dielectric susceptibility of
surrounding medium, the weak coupling regime holds at arbitrarily small
carrier concentrations. Localized electron-hole pairs are absent in graphene,
thus the behavior of the system versus coupling strength is
cardinally different from usual BCS-BEC crossover.
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