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 × 2e²/h in the absence of an applied magnetic field. We have studied the density- and temperature-dependent conductance of ultra low-disorder GaAs/Al_xGa_1−xAs quantum wires with nominal lengths l = 0, 0.5, and 2 μm, fabricated from structures free of the disorder associated with modulation doping. In a direct comparison in zero magnetic field we observe structure near 0.7 × 2e²/h for l = 0, whereas the l = 2 μm wires show structure evolving with increasing electron density to 0.5 × 2e²/h, the value expected for an ideal spin-split subband. For intermediate lengths (l = 0.5 μm) the feature at 0.7 × 2e²/h evolves to 0.55 × 2e²/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.