Magnetoresistance of composite fermions at ν = 1 / 2

We have studied temperature dependence of both diagonal and Hall resistivity in the vicinity of ν = 1/2. Magnetoresistance was found to be positive and almost independent of temperature: temperature enters resistivity as a logarithmic correction. At the same time, no measurable corrections to the Hall resistivity has been found. Neither of these results can be explained within the mean-field theory of composite fermions by an analogy with conventional low-field interaction theory. There is an indication that interactions of composite fermions with fluctuations of the gauge field may reconcile the theory and experiment. PACS numbers: 73.40.Hm Typeset using REVTEX ∗Present address: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544