Possible spin polarization in a one-dimensional electron gas

In zero magnetic field, conductance measurements of clean one-dimensional (1D) constrictions defined in GaAs/AlGaAs heterostructures show up to 26 quantized ballistic plateaus, as well as a structure close to 0.7(2e(2)/h). In an in-plane magnetic field all the 1D subbands show linear Zeeman splitting, and in the wide channel limit the g factor is \g\ = 0.4, close to that of bulk GaAs. For the last subband, spin splitting originates from the structure at 0.7(2e(2)/h), indicating spin polarization at B = 0. The measured enhancement of the g factor as the subbands are depopulated suggests that the ''0.7 structure'' is induced by electron electron interactions.