Excitonic superfluidity and screening in electron-hole bilayer systems

Superfluidity in electron-hole bilayers in graphene and GaAs has been predicted theoretically many times but not yet definitively observed. A key controversy is the correct approximation for the screening of the Coulomb interaction for the pairing. Mean-field theories using different approximations for the screening lead to diametrically contradictory predictions for superfluidity. We test these different approximations against diffusion quantum Monte Carlo results and find good agreement with the mean-field theory that uses screening in the superfluid state, but large discrepancies with other approximations for screening. This mean-field theory predicts no superfluidity in existing devices, provides pointers for new devices to generate the superfluidity, and, very importantly, it permits calculations for complicated lattices at finite temperatures, impractical in Monte Carlo.