MEASUREMENTS OF A COMPOSITE FERMION SPLIT-GATE

Recent theoretical and experimental work demonstrates that at filling factor nu=1/2, a two-dimensional electron gas can be described in term s of composite fermions (CFs), for which the effective magnetic field vanishes. We present low-temperature measurements on a wide split-gate (SG) device investigating CFs in the quantum point contact (QPC) defi ned by such a structure. Negative magnetoresistance due to suppression of backscattering in the QPC was observed both around zero magnetic f ield and nu=1/2. We have also measured the resistance of a CF QPC at z ero effective magnetic field as a function of gate voltage, with a com pensating field to maintain nu=1/2 in the QPC. Using a simple model, w e have determined the channel widths for CFs, which are narrower than those for electrons.