  We report conductance measurements of a ballistic one-dimensional (1D) wire
defined in the lower two-dimensional electron gas of a GaAs/AlGaAs double
quantum well. At low temperatures there is an additional structure at
$0.7(2e^2/h)$ in the conductance, which tends to $e^2/h$ as the electron
density is decreased. We find evidence for complete spin polarization in a
weakly disorderd 1D wire at zero magnetic field through the observation of a
conductance plateau at $e^2/h$, which strengthens in an in-plane magnetic field
and disappears with increasing electron density. In all cases studied, with
increasing temperature structure occurs at $0.6(2e^2/h)$. We suggest that the
0.7 structure is a many-body spin state excited out of, either the
spin-polarized electron gas at low densities, or the spin-degenerate electron
gas at high densities.
