FIG.57 Experimental electron focusi

FIG.57 Experimental electron focusing spectra (in the generalized longitudinal resistance configuration) at 0.3 K for five different injector-collector separations in a very high mobility material. The vertical scale varies among the curves. Taken from J. Spector et al., Surf. Sci. 228, 283 (1990). FIG.58 Exponential decay of the oscillation amplitude of the collector voltage (normalized by the injector voltage) as a function of injector-collector separation d (denoted by L in the text). Taken from J. Spector et al., Surf. Sci. 228, 283 (1990). FIG.59 Magnetoresistance of N constrictions in parallel at 1.3 K. The arrows indicate the oscillations due to electron focusing, according to the mechanisms illustrated in the inset. The resistance scale is indicated by 10 bars. Taken from K. Nakamura et al., Appl. Phys. Lett. 56, 385 (1990). FIG.60 Illustration of the collimation effect for an abrupt constriction (a) containing a potential barrier of height Ec and for a horn-shaped constriction (b) that is flared from a width Wmin to Wmax. The dash-dotted trajectories approaching at an angle α outside the injection/acceptance cone are reflected. Taken from H. van Houten and C. W. J. Beenakker, in “Nanostructure Physics and Fabrication” (M. Reed andW. P. Kirk, eds.). Academic, New York, 1989. FIG.61 Detection of a collimated electron beam over a distance of 4 μm. In this four-terminal measurement, two ohmic contacts to the 2DEG region between the point contacts are used: One of these acts as a drain for the current Ii through the injector, and the other is used as a zeroreference for the voltage Vc on the collector. The drawn curve is the experimental data at T = 1.8K. The black dots are the result of a semiclassical simulation, using a hard-wall potential with contours as shown in the inset. The dashed curve results from a simulation without collimation (corresponding to rectangular corners in the potential contour). Taken from L. W. Molenkamp et al., Phys. Rev. B 41, 1274 (1990).