Ballistic transport in one-dimensional bilayer hole systems

We have studied the ballistic transport properties of a one-dimensional (1D) channel created in a high mobility bilayer 2D hole system formed in a back-gated GaAs-AlGaAs heterostructure. We observe clean and robust conductance quantization in units of 2e2/h at dilution refrigerator base temperatures without the hysteresis and irregular oscillations that have hampered previous studies of 1D hole systems. In addition to the expected plateaus at multiples of G0=2e2/h, we also report the first observation of a clear step at 0.7×G0 for a 1D hole system. We observed ballistic transport in both the upper and lower quantum wires, with the strongest quantization obtained in the upper wire. The high stability of these devices and the clear conductance quantization has allowed us to measure the energy spacing of the 1D subbands, which is significantly smaller than for comparable electron systems, due to the large effective hole mass.