  Conductance measurements of carbon nanotubes containing gated local depletion
regions exhibit plateaus as a function of gate voltage, spaced by approximately
e2/h, the quantum of conductance for a single (non-degenerate) mode. Plateau
structure is investigated as a function of bias voltage, temperature, and
magnetic field. We speculate on the origin of this surprising quantization,
which appears to lack band and spin degeneracy.
