Ballistic electron transport in quasi-one-dimensional systems

Results of low-temperature resistance measurements performed upon short, narrow channels defined in the two-dimensional electron gas (2DEG) of GaAs-AlGaAs heterostructures are presented. The observed quantisation of resistance has been rigorously derived in recent theoretical models, notably the adiabatic model of electronic transport and the wide-narrow-wide geometry. The predictions of these two models are compared and their application to the experimental results is discussed. The application of a transverse magnetic field gives rise to the phenomenon of magnetic depopulation. A simple variational model has been used to model this behaviour and the derived results are contrasted with previous calculations. The additional spin-split plateaux observed in a parallel magnetic field have been used to determine the Landé g-factor and suggest that there is little or no enhancement. Results are also presented for a device which manifested oscillatory behaviour as a function of applied gate voltage and the observed Aharonov-Bohm oscillations have been used to characterise the device. The non-ohmic addition of resistance which has been observed in structures with two defined constrictions is discussed within the context of a recent theoretical model and is explained in terms of the adiabatic motion of electrons through the channel constriction.