Exciton BCS or BEC state in a semiconductor bilayer system?
  We calculate the off-diagonal long range order (ODLRO) terms of the exciton--exciton correlation function of a semiconductor bilayer system with Coulomb interaction and a transverse magnetic field. We show that the formation of a BEC state is very sensitive to the width of the interaction in momentum space. This dependence is analytically derived and represents the key physical ingredient for the formation (or not) of an exciton condensate state. 
E. H. Martins Ferreira, Tathiana Moreira, M. C. Nemes