Quantized conductance in an AlAs two-dimensional electron system quantum point contact

We report experimental results on a quantum point contact (QPC) device formed in a wide AlAs quantum well where the two-dimensional electrons occupy two in-plane valleys with elliptical Fermi contours. To probe the closely-spaced, one-dimensional electric subbands, we fabricated a point contact device defined by shallow etching and a top gate that covers the entire device. The conductance versus top gate bias trace shows a series of weak plateaus at integer multiples of 2e²∕h, indicating a broken valley degeneracy in the QPC and implying the potential use of QPC as a simple ``valley filter'' device. A model is presented to describe the quantized energy levels and the role of the in-plane valleys in the transport. We also observe a well-developed conductance plateau near 0.7×2e²∕h which may reflect the strong electron-electron interaction in the system.