Composite Fermion Geometric Resonance Near �� = 1/2 Fractional Quantum Hall State

We observe geometric resonance features of composite fermions on the flanks of the even denominator �� = 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 �� = 1/2 the system stays single-component and supports a composite fermion Fermi sea before transitioning into a �� = 1/2 fractional quantum Hall state, presumably the two-component ��331 state.