  Superfluidity in e-h bilayers in graphene and GaAs has been predicted many
times but not observed. A key problem is how to treat the screening of the
Coulomb interaction for pairing. Different mean-field theories give
dramatically different conclusions, and we test them against diffusion
Monte-Carlo calculations. We get excellent agreement with the mean-field theory
that uses screening in the superfluid state, but large discrepancies with the
others. The theory predicts no superfluidity in existing devices and gives
pointers for new devices to generate superfluidity.
