Geometric Resonance of Composite Fermions Near the ν=1/2 Fractional Quantum Hall State.

: We observe geometric resonance features of composite fermions on the flanks of the even-denominator ν=1/2 fractional quantum Hall state in high-mobility two-dimensional electron and hole systems confined to wide GaAs quantum wells and subjected to a weak, strain-induced, unidirectional periodic potential modulation. The features provide a measure of how close to ν=1/2 the system stays single-component and supports a composite fermion Fermi sea before transitioning into a ν=1/2 fractional quantum Hall state, presumably, the two-component Ψ331 state.