Measurements of a composite fermion split-gate device

Recent theoretical and experimental work demonstrates that a two-dimensional electron gas at Landau-level filling factor nu=1/2 can be described in terms of composite fermions (CF's) for which the effective magnetic field B-eff vanishes. We have measured the transport properties of CF's in a quantum point contact (QPC) defined by a wide split-gate device. Negative magnetoresistance due to suppression of backscattering in the QPC was observed both around zero magnetic field B=0 and B-eff=0. We have also measured the resistance of a composite fermion QPC at B-eff=0 as a function of gate voltage; with an applied magnetic field to maintain nu=1/2 in the QPC. Using a simple model to compare the results for B=0 and nu=1/2, we have determined that the channel widths for CF's are narrower than those for electrons