  We show theoretically that excitons can form from spatially separated
one-dimensional ground state populations of electrons and holes, and that the
resulting excitons can form a quasicondensate. We describe a mean-field
Bardeen-Cooper-Schrieffer theory in the low carrier density regime and then
focus on the core-shell nanowire giving estimates of the size of the excitonic
gap for InAs/GaSb wires and as a function of all the experimentally relevant
parameters. We find that optimal conditions for pairing include small overlap
of the electron and hole bands, large effective mass of the carriers, and low
dielectric constant of the surrounding media. Therefore, one-dimensional
systems provide an attractive platform for the experimental detection of
excitonic quasicondensation in zero magnetic field.
