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Using a cryogenic scanned probe microscope (SPM) one can locally modify the sheet density of a two-dimensional electron gas (2DEG), and image the ballistic flow of electrons through a point contact in the 2DEG located beneath the surface of a GaAs/AlGaAs heterostructure. We calculate the capacitively induced change in sheet density when a charged SPM tip is brought into contact with a semiconductor heterostructure containing a two-dimensional electron gas. A simple scattering model, based on a local change in sheet density, is used to analyze experimental data taken with the SPM method described above.

We report on observations of coherent backscattering in open devices consisting of a quantum point contact and two reflector gates. The devices are fabricated in a high-mobility two-dimensional electron gas system, and magnetotransport data are taken at a temperature of 385 mK. Unlike ballistic microstructures in which this effect has previously been measured, our devices are designed to yield many backscattered trajectories enclosing very similar areas. An array of these devices has been measured in order to average away magnetoconductance fluctuations.

We have utilized the the weak localization effect in a narrow channel to measure the phase coherence time (τφ) at temperatures between 0.42 K and 4.25 K for electrons in a two-dimensional electron gas formed in a GaAs/Al_xGa_1-xAs heterostructure. The measured values agree well with electron-electron scattering theory in a one-dimensional channel including both single particle and collective contributions. Copyright 1994, 1999 Academic Press