  We predict enhanced electron-hole superfluidity in two coupled electron-hole
armchair-edge terminated graphene nanoribbons separated by a thin insulating
barrier. In contrast to graphene monolayers, the multiple subbands of the
nanoribbons are parabolic at low energy with a gap between the conduction and
valence bands, and with lifted valley degeneracy. These properties make
screening of the electron-hole interaction much weaker than for coupled
electron-hole monolayers, thus boosting the pairing strength and enhancing the
superfluid properties. The pairing strength is further boosted by the
quasi-one-dimensional quantum confinement of the carriers, as well as by the
large density of states near the bottom of each subband. The latter magnifies
the superfluid shape resonances caused by the quantum confinement. Several
superfluid partial condensates are present for finite-width nanoribbons with
multiple subbands. We find that superfluidity is predominately in the
strongly-coupled BEC and BCS-BEC crossover regimes, with large superfluid gaps
up to 100 meV and beyond. When the gaps exceed the subband spacing, there is
significant mixing of the subbands, a rounding of the shape resonances, and a
resulting reduction in the one-dimensional nature of the system.
