Multicomponent Superfluidity and Screening in Biased Electron-Hole Double Bilayer Graphene with Realistic Bands.

Superfluidity has recently been reported in double electron-hole bilayer graphene. The multiband nature of the bilayers is expected to be very important because the band gaps between conduction and valence bands are small. Here we report on a detailed mean-field study that takes into account the effects of multichannel electron-hole pairing, including Josephson-like pair transfer between bands; screening from both intraband and interband excitations; and effects of the non-parabolic band dispersion that accompanies the variable band gaps in bilayer graphene. From the self-consistent calculation based on the random phase approximation in superfluid state, we obtain a density range for superfluidity consistent with the density range reported in the recent experiments. We find for non-zero gaps, that the boost of the density of states from the flattening of the bands strengthens the superfluidity. We also find that the superfluidity modifies the intraband screening in a fundamentally different way from the interband screening. Surprisingly, the net effect of the screening is to restrict the superfluid pairing entirely to the conduction band - even for very small band gaps. This makes the system behave almost analogously to a one-band superfluid.