Figure 66 shows the precursor of th

Figure 66 shows the precursor of the classical Hall plateau (the 乬last plateau乭) in a relatively wide Hall cross. The experimental data (solid curve) is from a paper by Simmons et al.178 The semiclassical calculation (dashed curve) is for a square-well confining potential of channel width W = 0.8 兪m (as estimated in the experimental paper) and with the relatively sharp corners shown in the inset. The Fermi energy used in the calculation is EF = 14meV, which corresponds (via ns = EFm/兾丳h2) to a sheet density in the channel of ns = 3.9 亊 1015m.2, somewhat below the value of 4.9 亊 1015m.2 of the bulk material in the experiment. Good agreement between theory and experiment is seen in Fig. 66. Near zero magnetic field, the Hall resistance in this geometry is close to the linear result RH = B/ens for a bulk 2DEG (dotted line). The corners are sufficiently smooth to generate a Hall plateau via the guiding mechanism discussed in Section III.E.1. The horn collimation effect, however, is not sufficiently large to suppress RH at small B. Indeed, the injection/acceptance cone for this junction is considerably wider (about 115.) than the maximal angular opening of 90. required for quenching of the Hall effect via the scrambling mechanism describedin Section III.E.1.