Properties of a ballistic quasi-one-dimensional constriction in a parallel high magnetic field

We have investigated the magnetic properties of a ballistic quasi-one-dimensional channel, in a GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunction, when the magnetic field is applied in the plane of the two-dimensional electron gas. At high magnetic fields, and high applied source-drain voltage, the devices show differential conductance plateaus quantized in units of ${\mathit{e}}^2$/2h. This is a consequence of the combined effect of the electric field, which causes the number of conducting subbands to be different in the two current directions, and the Zeeman splitting of the one-dimensional subbands. When the magnetic field is parallel to the current direction, the g factor is 1.1±0.1; and when the field is perpendicular to the current, the g factor is reduced.