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Spin splitting of conduction band electrons in In0.53Ga0.47As/In0.77Ga0.23As/InP heterostructures due to spin-orbit coupling is studied by performing Shubnikov–de Haas measurements on nongated and gated Hall bars. From an analysis of the beating pattern in the Shubnikov–de Haas oscillations, the spin-orbit coupling constant is determined. For a symmetric sample no beating pattern and thus no spin splitting is observed. This demonstrates that the k3 contribution to the spin-orbit coupling constant can be neglected. By applying an envelope function theory it is shown that the major contribution to the Rashba spin-orbit coupling originates from the band offset at the interface of the quantum well. Using gated Hall bar structures it is possible to alter the spin-orbit coupling by application of an appropriate gate voltage. A more negative gate voltage leads to a more pronounced asymmetry of the quantum well, which gives rise to a stronger spin-orbit coupling.

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We have observed quantum interference in the electronic transport in a T-shaped Al 0.3 Ga 0.7 As/GaAs heterostructure. The geometry is defined by four independent Schottky gates on top of the layer system. By changing the split-gate voltages, the dimensions of the T-shaped two-dimensional electron gas could be varied continuously. Especially, the stub length of the transistor can be controlled in order to switch between constructive and destructive interference. An additional advantage of using gates instead of etching methods to define the geometry is the smooth form of the boundary potential which implies specular boundary scattering. At low temperatures the transport in the high mobility two-dimensional electron gas ͑2DEG͒ is ballistic. Thus weaklocalization effects and conductance fluctuations are suppressed, whereas the intended interference pattern is reproducible and nearly identical for different samples. We attribute the observed resistance oscillations to the change in transmissivity in the device when the geometry is altered. Other explanations are discussed as well but could be excluded by experiment.

Electron-electron scattering of ballistic electrons in a two-dimensional electron gas was studied as a function of the electron excess energy above the Fermi energy and of temperature. At low temperatures of 1.4 K it is found that for excess energies of approximately 30% of the Fermi energy the electrons in a ballistic electron beam are already scattered significantly due to electron-electron interaction. A very good agreement between our experimental data and theory was found, when the measured data were compared with numerical calculations based on a theory of Giuliani and Quinn [Phys. Rev. B 26, 4421 (1982)], while the agreement was only poor for the analytical approximation of the electron-electron scattering rate.