Abstract
We have measured the magnetoresistance of a variety of structures to
search for effects associated with composite fermions (CF) near the Landau filling factor v = 1/2. We find evidence for effects due to
randomization of semiclassical ballistic CF trajectories. These produce
magnetoresistance features similar to those observed near zero magnetic
field. However, we were not able to reproduce the recent CF magnetic
focusing experiment despite using devices of very similar quality to
those used in the original experiment. We also searched, without
success, for phenomena due to phase coherence of CF. The relative ease
with which the various magnetoresistance effects are seen in CF is
discussed, in part with the aid of semiclassical simulations. It is
discovered that inhomogeneities of carrier density cause the
magnetoresistance anomalies to be smeared out, largely as a result of
spatial variations in the effective magnetic field experienced by the
CF. We find also that experiments which are based on randomization of
trajectories are more resilient to this spatial variation.
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