Zero length quantum wires (or point contacts) exhibit unexplained conductance structure close to 0.7 X 2e^2/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 mu m, fabricated from structures free of the disorder associated with modulation doping. In a direct comparison we observe structure near 0.7 X 2e^2/h for l=0 whereas the l=2 mu m wires show structure evolving with increasing electron density to 0.5 X 2e^2/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.
@article{arxiv.cond-mat/0001174,
title = {Many-body spin related phenomena in ultra-low-disorder quantum wires},
author = {D. J. Reilly and G. R. Facer and A. S. Dzurak and B. E. Kane and R. G. Clark and P. J. Stiles and J. L. O'Brien and N. E. Lumpkin and L. N. Pfeiffer and K. W. West},
journal= {arXiv preprint arXiv:cond-mat/0001174},
year = {2007}
}