Superfluidity of dipole excitons in two layers of gapped graphene
  A study of the formation of excitons as a problem of two Dirac particles confined in two-layer graphene sheets separated by a dielectric when gaps are opened and they interact via a Coulomb potential is presented. We propose to observe Bose-Einstein condensation and superfluidity of quasi-two-dimensional dipole excitons in double layer graphene in the presence of band gaps. The energy spectrum of the collective excitations, the sound spectrum, and the effective exciton mass are functions of the energy gaps, density and interlayer separation. The superfluid density ns and temperature of the Kosterlitz-Thouless phase transition Tc are decreasing functions of the energy gaps as well as the interlayer separation, and therefore, could be controlled by these parameters. 
Oleg L. Berman, Roman Ya. Kezerashvili, Klaus G. Ziegler
cond-mat.mes-hall