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

We observe fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor $ν=1/2$ in two-dimensional hole systems confined to GaAs quantum wells of width 30 to 50 nm and having bilayer-like charge distributions. The $ν=1/2$ 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 $ν=1/2$ FQHE to be consistent with a two-component, Halperin-Laughlin ($Ψ_{331}$) state.