COMPOSITE FERMIONS AND LANDAU-LEVEL MIXING IN THE FRACTIONAL QUANTUM HALL-EFFECT

The reduction of the energy gap due to Landau-level mixing, characteri zed by the dimensionless parameter lambda=(e(2)/epsilon l(0))/h omega( c), has been calculated by variational Monte Carlo for the fractional quantum Hall effect at filling fractions v=1/3 and 115 using a modifie d version of Jain's composite-fermion wave functions. These wave funct ions exploit the Landau-level mixing already present in composite-ferm ion wave functions by introducing a partial Landau-level projection op erator. Results for the energy gaps are consistent with experimental o bservations in n-type GaAs, but we conclude that Landau-level mixing a lone cannot account for the significantly smaller energy gaps observed in p-type systems.