Fractional Quantum Hall Effect at ν=1/2 in Hole Systems Confined to GaAs Quantum Wells

We observe the fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor nu = 1/2 in two-dimensional hole systems confined to GaAs quantum wells of width 30 to 50 nm and having bilayerlike charge distributions. The nu = 1/2 FQHE is stable when the charge distribution is symmetric and only in a range of intermediate densities, qualitatively similar to what is seen in two-dimensional electron systems confined to approximately twice wider GaAs quantum wells. Despite the complexity of the hole Landau level structure, originating from the coexistence and mixing of the heavy-and light-hole states, we find the hole nu = 1/2 FQHE to be consistent with a two-component, Halperin-Laughlin (Psi(331)) state.