Many-body spin-related phenomena in ultra low-disorder quantum wires

Zero length quantum wires (or point contacts) exhibit unexplained conductance 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 associated 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 value 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 region.