Key points are not available for this paper at this time.
Conductance quantization in the absence and in the presence of a magnetic field is discussed for a split-gate constriction with a local potential at the bottleneck forming a saddle. Simple criteria for the occurrence of conductance steps and the accuracy of quantization are given in terms of the curvatures of the saddle.
Μ. Büttiker (Sun,) studied this question.