Quantized conductance in an AlAs 2D electron system quantum point contact

We report experimental results on a quantum point contact (QPC) device fabricated in a wide AlAs quantum well where the electrons occupy two conduction-band valleys with in-plane, elliptical Fermi contours. To probe the closely-spaced, one-dimensional, electric subbands (channels), we fabricated a QPC structure where the point contact is defined by a split-etched region covered by a global top gate. The conductance versus top gate bias trace shows a series of weak plateaus at every 2$e^{2}$/$h$, consistent with the fact that the one-dimensional confinement and the anisotropy of the Fermi contours break the valley degeneracy for the QPC channels. Moreover, we observe a ``0.7 structure'' which is much better developed than the 2$e^{2}$/$h$ plateaus, possibly reflecting the stronger electron-electron interaction in this system because of the larger electron effective mass.