Composite fermions and Landau-level mixing in the fractional quantum Hall effect

The reduction of the energy gap due to Landau-level mixing, characterized by the dimensionless parameter λ=(${\mathit{e}}^2$/ε${\mathit{l}}_0$)/ħ${\mathrm{\omega }}_{\mathit{c}}$, has been calculated by variational Monte Carlo for the fractional quantum Hall effect at filling fractions ν=1/3 and 1/5 using a modified version of Jain’s composite-fermion wave functions. These wave functions exploit the Landau-level mixing already present in composite-fermion wave functions by introducing a partial Landau-level projection operator. Results for the energy gaps are consistent with experimental observations in n-type GaAs, but we conclude that Landau-level mixing alone cannot account for the significantly smaller energy gaps observed in p-type systems.