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 $\nu =\frac{1}{2}$ can be described in terms of composite fermions (CF's) for which the effective magnetic field $B_{\mathrm{eff}}$ 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 $B=0\mathrm{}$ and $B_{\mathrm{eff}}=0\mathrm{}$. We have also measured the resistance of a composite fermion QPC at $B_{\mathrm{eff}}=0\mathrm{}$ as a function of gate voltage, with an applied magnetic field to maintain $\nu =\frac{1}{2}$ in the QPC. Using a simple model to compare the results for $B=0\mathrm{}$ and $\nu =\frac{1}{2}$, we have determined that the channel widths for CF's are narrower than those for electrons.