Zero length quantum wires (or point contacts) exhibit unexplained conductan
ce structure close to 0.7 x 2e(2)/h in the ab sen ce of an applied magnetic
field. We have studied the density- and temperature-dependent conductance
of ultra low-disorder GaAs/AlxGa1-xAs quantum wires with nominal lengths l=
0, 0.5, and 2 mum, fabricated from structures free of the disorder associat
ed with modulation doping. In a direct comparison in zero magnetic field we
observe structure near 0.7x2e(2)/h for l=0, whereas the l=2 mum wires show
structure evolving with increasing electron density to 0.5x2e(2)/h, the va
lue expected for an ideal spin-split subband. For intermediate lengths (l=0
.5 mum) the feature at 0.7x2e(2)/h evolves to 0.55x2e(2)/h with increasing
density. Our results suggest the dominant mechanism through which electrons
interact can be strongly affected by the length of the one-dimensional reg
ion.