MEASUREMENTS OF A COMPOSITE FERMION SPLIT-GATE DEVICE

Recent theoretical and experimental work demonstrates that a two-dimen sional electron gas at Landau-level filling factor nu=1/2 can be descr ibed in terms of composite fermions (CF's) for which the effective mag netic 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 backscatterin g in the QPC was observed both around zero magnetic field B=0 and B-ef f=0. We have also measured the resistance of a composite fermion QPC a t B-eff=0 as a function of gate voltage; with an applied magnetic fiel d to maintain nu=1/2 in the QPC. Using a simple model to compare the r esults for B=0 and nu=1/2, we have determined that the channel widths for CF's are narrower than those for electrons.