The sample geometry is that of Fig.

The sample geometry is that of Fig. 82. In Fig. 86 the four-terminal longitudinal resistance RL and Hall resistance RH are shown for both a small voltage (−0.3 V) and a large voltage (−2.5 V) on the gate defining the constriction. The longitudinal resistance decreases in weak fields because of reduction of backscattering, as discussed in Section III.B.2. At larger fields Shubnikov-De Haas oscillations develop. The data for Vg = −0.3V exhibit zero minima in the Shubnikov-De Haas oscillations in RL and the normal quantum Hall resistance RH = (h/2e2)N−1 wide, determined by the number of Landau levels occupied in the wide regions (Nwide can be obtained from the quantum Hall effect measured in the absence of the constriction or from the periodicity of the Shubnikov-De Haas oscillations).