In the high-field regime the point contact geometry of Fig. 81 is essentially equivalent to a geometry in which a potential barrier is present across the entire width of the Hall bar (created by means of a narrow continuous gate). The latter geometry was studied by Haug et al.340 and by Washburn et al.339 The geometries of both experiments339,340 are the same (see Figs. 84 and 85), but the results exhibit some interesting differences because of the different dimensions of gate and channel.