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

• Received 26 April 2015

DOI:https://doi.org/10.1103/PhysRevLett.114.236406