Abstract
We observe quantized conductance in 2- to 10-µ m-long wires formed in a very-high-mobility modulation-doped heterostructure. These wires have a new gate configuration that facilitates strong lateral constriction despite the large separation between the surface and the electron channel. Random potential scattering in the wire causes a conductance dip near the threshold of the higher-lying subband. This scattering is strongly suppressed when only the ground subband is occupied. Wires longer than 20 µ m display a conductance step of 0.6 to 0.7 (2e2/h). This step is probably made more evident by the effect of thermal broadening as well as by a dip in the conductance near the threshold for the higher-lying subband.