We discuss quantization of the conductance in short, ultraclean one-dimensional quantum wires of a design where an electron gas is induced electrostatically. Two-level sets of gates allow independent control of electron density in the constriction and in the reservoirs, thus varying the conductance G as a function of the bias on the gates G(Vtg,Vsg). Up to 12 clean well-resolved conductance G(Vsg) plateaus confirm the high quality of the constriction. The experimental curves are modeled using three-dimensional self-consistent calculations in the Thomas–Fermi approximation of the electrostatic potential of the constriction and solution of the two-dimensional problem of electron transport in the calculated potential. Our calculations are in qualitative agreement with the experiment.

We have performed four-terminal conductance measurements of a one-dimensional (1D) channel in which it is possible to modulate the potential profile using three overlaying finger gates. In such a 1D ballistic structure we have observed that the conductance steps show a gradual decrease from 2e 2 / h to 0.97ϫ 2e 2 / h with increasing negative finger gate voltage in a short, clean 1D constriction. We suggest this phenomenon is due to differing shifts of 1D subbands with changing spilt-gate voltage. Both a simple analytical estimate for an adiabatic constriction and a realistic modeling of the device give the same magnitude of the conductance decrease as observed in our experiments.

Low-temperature transport properties of a lateral quantum dot formed by overlaying finger gates in a clean one-dimensional channel are investigated. Continuous and periodic oscillations superimposed upon ballistic conductance steps are observed, when the conductance G of the dot changes within a wide range 0 < G < 6e 2 /h. Calculations of the electrostatics confirm that the measured periodic conductance oscillations correspond to successive change of the total charge of the dot by e. By modelling the transport it is shown that the progression of the Coulomb oscillations into the region G > 2e 2 /h may be due to suppression of inter-1D-subband scattering. Fully transmitted subbands contribute to coherent background of conductance, while sequential tunneling via weakly transmitted subbands leads to Coulomb charging of the dot. 73.40.Gk, 73.20.Dx

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