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(2e²/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 g0ex0ex=0ex0ex0.4, close to that of bulk GaAs. For the last subband, spin splitting originates from the structure at 0.7(2e²/h), indicating spin polarization at B0ex0ex=0ex0ex0. The measured enhancement of the g factor as the subbands are depopulated suggests that the ``0.7 structure'' is induced by electron-electron interactions.