Many-body Spin Interactions in Semiconductor 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/AlGaAs quantum wires with nominal lengths l = 0 and 2 μm, fabricated from structures free of the disorder associated with modulation doping. In a direct compansion 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 in zero magnetic field, the value expected for an ideal spin-split sub-band. Our results suggest the dominant mechanism through which electrons interact can be strongly affected by the length of the 1D region.