INTERACTION EFFECTS IN A ONE-DIMENSIONAL CONSTRICTION

We have investigated the transport properties of one-dimensional (1D) constrictions defined by split-gates in high quality GaAs/AlxGa1-xAs h eterostructures. In addition to the usual quantized conductance platea us, the equilibrium conductance shows a structure close to 0.7(2e(2)/h ), and in consolidating our previous work [K. J. Thomas at al., Phys. Rev. Lett. 77, 135 (1996)] this 0.7 structure has been investigated in a wide range of samples as a function of temperature, carrier density , in-plane magnetic field B-parallel to, and source-drain voltage V-sd . We show that the 0.7 structure is not due to transmission or resonan ce effects, nor does it arise from the asymmetry of the heterojunction in the growth direction. All the 1D subbands show Zeeman splitting at high B-parallel to and in the wide channel limit the g factor is \g\a pproximate to 0.4, close to that of bulk GaAs. As the channel is progr essively narrowed we measure an exchange-enhanced g factor. The measur ements establish that the 0.7 structure is related to spin, and that e lectron-electron interactions become important for the last few conduc ting 1D subbands.