An experimental analysis of the fractional quantum Hall eKect is described in which oscillations in p are treated as Shubnikov-de Haas oscillatlons of the composite fermions (CF) formed by a flux attachment transformation. We find a CF effective mass of 0.5m, at zero effective field which increases weakly with effective magnetic field at a rate independent of carrier density. The CF quantum scattering times are the saxne as for the underlying single particle electron states.

The critical filling factor ν c where Shubnikov-de Haas oscillations become spin split is investigated for a set of GaAs-GaAlAs heterojunctions. Finite temperature magnetoresistance measurements are used to extract the value of ν c at zero temperature. The critically point is where the disorder potential has the same magnitude as the exchange energy, leading to the empirical relationship ν c = g * n e τ s h/2m 0 . This is valid for all the samples studied, where the density n e and single particle lifetime τ s both vary by more than an order of magnitude and g * the exchange enhanced g-factor has a weak dependence on density. For each sample the spin gap energy shows a linear increase with magnetic field. Experiments in tilted magnetic field show the spin gap is the sum of the bare Zeeman energy and an exchange term. This explains why measurements of the enhanced g-factor from activation energy studies in perpendicular field and the coincidence method in tilted fields have previously disagreed.