EVIDENCE FOR QUASI-CLASSISAL TRANSPORT OF COMPOSITE FERMIONS IN AN INHOMOGENEOUS EFFECTIVE MAGNETIC-FIELD

We report on transverse magnetic focusing experiments in arrays of equ idistant constrictions with centre-to-centre constriction spacings L v arying from 500 nm to 1.2 mu m in the vicinity of the Landau level fil ling factor nu = 1/2 of a two-dimensional electron system. Provided th e composite fermion mean free path is comparable to L, focusing is obs erved for both effective magnetic field directions. The non-uniform el ectron distribution with a saddle point in the middle of each construc tion, and the associated inhomogeneous effective magnetic field for th e composite fermions, invokes characteristic differences in the compos ite fermion focusing spectra compared with the electron focusing spect ra near zero magnetic field. These changes are well predicted by quasi -classical calculations of the composite fermion dynamics in the corre sponding potential landscape.